1. Introduction
Transcription is the process through which information encoded in DNA is copied into RNA. Although RNA polymerase is the central enzyme responsible for RNA synthesis, transcription does not occur through RNA polymerase alone. A large collection of proteins and regulatory DNA sequences work together to identify genes, recognize promoters, open chromatin, recruit RNA polymerase, initiate RNA synthesis, regulate elongation, and terminate transcription.
The proteins involved in controlling transcription are collectively referred to as transcription factors, whereas the collection of proteins and molecular components required for transcription is referred to as the transcription machinery.
Transcription factors and transcription machinery are particularly complex in eukaryotic organisms because DNA is packaged into chromatin. Before RNA polymerase can access many genes, chromatin structure must be appropriately modified or remodeled.
A simplified view of the process is:
Regulatory signal → Transcription factor activation → DNA recognition → Chromatin modification → Transcription machinery assembly → RNA polymerase recruitment → RNA synthesis
Thus, transcription factors act as important molecular regulators, while the transcription machinery provides the molecular apparatus required to synthesize RNA.
2. Transcription Factors
2.1 Definition
A transcription factor is a protein that regulates gene transcription by interacting with specific DNA sequences, RNA polymerase, or other proteins associated with transcription.
Transcription factors can either:
- activate transcription,
- repress transcription,
- regulate the assembly of transcription machinery,
- modify chromatin accessibility,
- regulate transcriptional elongation.
They allow cells to express genes according to their developmental stage, tissue type, environmental conditions, and physiological requirements.
2.2 Importance of Transcription Factors
The genome contains thousands of genes, but all genes are not active simultaneously.
For example, a neuron and a liver cell generally contain essentially the same genome, yet they perform very different functions. This difference is largely produced by differences in gene-expression patterns.
Transcription factors contribute to this selective gene expression by determining which genes are active and which remain inactive.
2.3 Major Classes of Transcription Factors
Transcription factors can broadly be classified into:
- General transcription factors
- Sequence-specific transcription factors
- Activators
- Repressors
- Pioneer transcription factors
- Signal-dependent transcription factors
These categories can overlap because one transcription factor may possess more than one regulatory role.
3. General Transcription Factors
3.1 Definition
General transcription factors are proteins required for transcription initiation by specific RNA polymerases.
For protein-coding genes transcribed by RNA polymerase II, general transcription factors assemble at the promoter to form the transcription initiation machinery.
They help:
- recognize the promoter,
- position RNA polymerase II,
- open DNA,
- initiate RNA synthesis,
- transition RNA polymerase into productive elongation.
3.2 Major General Transcription Factors
Important general transcription factors associated with RNA polymerase II include:
- TFIID
- TFIIA
- TFIIB
- TFIIF
- TFIIE
- TFIIH
Each performs specific functions during formation and activation of the transcription initiation complex.
4. TFIID
4.1 Structure
TFIID is one of the first major general transcription-factor complexes involved in RNA polymerase II transcription initiation.
It consists mainly of:
- TATA-binding protein (TBP)
- TBP-associated factors (TAFs)
4.2 TATA-Binding Protein
TBP recognizes and binds the TATA box when a TATA element is present in the promoter.
TBP binding causes significant bending of DNA.
This bending helps create a platform for recruitment and organization of other transcription factors.
4.3 TBP-Associated Factors
TAFs interact with promoter elements, transcription factors, and other components of the transcription machinery.
They help TFIID recognize and respond to different promoter environments.
Importantly, many promoters do not contain a canonical TATA box, so TAFs and other promoter-recognition mechanisms are important for transcription from such promoters.
5. TFIIA
TFIIA interacts with TFIID and helps stabilize the association of TFIID with promoter DNA.
It can also assist in counteracting certain inhibitory influences on TBP.
Therefore, TFIIA contributes to the formation of a stable transcription initiation complex.
6. TFIIB
6.1 Function
TFIIB acts as an important bridge between promoter-bound TFIID and RNA polymerase II.
It helps:
- position RNA polymerase II,
- establish the transcription start site,
- organize the initiation complex.
TFIIB therefore plays an important role in determining the proper location from which RNA synthesis begins.
7. TFIIF
TFIIF associates with RNA polymerase II.
Its functions include:
- assisting recruitment of RNA polymerase II,
- reducing nonspecific interactions of polymerase with DNA,
- stabilizing the initiation complex,
- participating in the transition from initiation to elongation.
8. TFIIE
TFIIE recruits and regulates TFIIH.
Therefore, although TFIIE does not itself carry out all the enzymatic activities required for promoter opening, it is important for bringing the appropriate machinery to the promoter.
9. TFIIH
TFIIH is a multifunctional complex with important roles in transcription initiation.
9.1 DNA Opening
TFIIH contains ATP-dependent activities that contribute to opening promoter DNA around the transcription start site.
9.2 RNA Polymerase II Phosphorylation
TFIIH contains a kinase activity that phosphorylates the C-terminal domain (CTD) of RNA polymerase II.
This phosphorylation is important for the transition of RNA polymerase II from initiation toward productive transcription.
9.3 Role in DNA Repair
TFIIH also participates in nucleotide excision repair.
Thus, TFIIH provides an important connection between transcription and DNA repair.
10. Sequence-Specific Transcription Factors
10.1 Definition
Sequence-specific transcription factors recognize particular DNA sequences and regulate nearby or distant genes.
Unlike general transcription factors, they are not required for every RNA polymerase II promoter.
They determine which genes should be expressed under particular cellular conditions.
10.2 DNA Recognition
Sequence-specific transcription factors contain specialized DNA-binding domains.
These domains recognize specific nucleotide sequences in promoters, enhancers, silencers, or other regulatory regions.
10.3 Regulatory Domains
Many transcription factors contain separate functional regions.
A typical transcription factor can contain:
DNA-binding domain + regulatory domain + protein-interaction domain
The DNA-binding domain recognizes DNA, while other regions interact with transcription machinery or regulatory proteins.
11. DNA-Binding Domains of Transcription Factors
Several structural motifs allow transcription factors to interact with DNA.
Important examples include:
- Zinc fingers
- Homeodomains
- Helix-turn-helix domains
- Basic helix-loop-helix domains
- Leucine zipper domains
12. Zinc-Finger Transcription Factors
12.1 Structure
Zinc-finger proteins contain structural motifs stabilized by zinc ions.
Different types of zinc-finger domains recognize different DNA sequences.
12.2 Function
Zinc-finger transcription factors can regulate genes involved in:
- development,
- differentiation,
- metabolism,
- cellular signaling.
Steroid hormone receptors are important examples of transcription factors containing zinc-finger DNA-binding domains.
13. Homeodomain Transcription Factors
13.1 Definition
A homeodomain is a DNA-binding domain of approximately 60 amino acids found in many developmental regulators.
13.2 Biological Role
Homeodomain-containing transcription factors are especially important in developmental processes.
They regulate gene-expression programs that determine:
- body patterning,
- tissue identity,
- cell differentiation.
14. Basic Helix-Loop-Helix Proteins
14.1 Structure
Basic helix-loop-helix proteins contain:
- a basic region involved in DNA binding,
- two α-helices,
- a flexible loop connecting the helices.
14.2 Function
These proteins often regulate developmental and differentiation pathways.
They can form dimers with other bHLH proteins, which influences their DNA-binding specificity and regulatory activity.
15. Leucine Zipper Proteins
15.1 Structure
Leucine zipper proteins contain regularly spaced leucine residues that facilitate protein dimerization.
A commonly discussed example is the basic leucine zipper (bZIP) family.
15.2 Function
Dimerization allows transcription factors to bind DNA and regulate gene expression.
Different combinations of protein partners can produce different regulatory outcomes.
16. Transcriptional Activators
16.1 Definition
A transcriptional activator is a regulatory protein that increases transcription of a target gene.
16.2 Mechanism
An activator can bind to an enhancer or promoter-proximal regulatory sequence.
It can then recruit:
- coactivators,
- chromatin-remodeling complexes,
- histone-modifying enzymes,
- Mediator,
- general transcription factors,
- RNA polymerase II-associated machinery.
This increases the probability of productive transcription.
17. Transcriptional Repressors
17.1 Definition
A transcriptional repressor decreases gene transcription.
17.2 Mechanisms of Repression
Repressors can function by:
- blocking activator binding,
- interfering with transcription-factor interactions,
- recruiting corepressors,
- recruiting histone deacetylases,
- promoting compact chromatin,
- interfering with RNA polymerase recruitment.
Thus, repression can occur through direct inhibition or through modification of chromatin.
18. Pioneer Transcription Factors
18.1 Definition
Pioneer transcription factors are specialized transcription factors capable of recognizing target DNA sequences even when those sequences are located within relatively inaccessible chromatin.
18.2 Function
They can help initiate changes in chromatin accessibility and facilitate binding of additional regulatory proteins.
This makes pioneer factors important during:
- development,
- differentiation,
- cell-fate determination.
19. Signal-Dependent Transcription Factors
Cells constantly receive signals from their surroundings.
These signals can activate transcription factors.
Examples include transcription factors responding to:
- hormones,
- growth factors,
- stress,
- inflammatory signals,
- nutrient availability.
The basic pathway is:
Signal → receptor/pathway → transcription-factor activation → DNA binding → gene expression
20. Transcription Machinery
20.1 Definition
The transcription machinery refers to the collection of proteins and molecular components required for transcription.
It includes:
- RNA polymerase,
- general transcription factors,
- promoter-recognition proteins,
- Mediator,
- chromatin-remodeling complexes,
- regulatory proteins,
- elongation factors,
- termination and RNA-processing factors.
The exact composition varies according to the organism, RNA polymerase, gene, and stage of transcription.
21. RNA Polymerase
21.1 Central Role
RNA polymerase is the catalytic core of transcription machinery.
It reads the DNA template and synthesizes RNA.
It catalyzes phosphodiester-bond formation between ribonucleotides.
21.2 RNA Polymerase II
RNA polymerase II is responsible for transcription of most protein-coding genes in eukaryotic cells.
It also synthesizes several classes of regulatory and non-coding RNAs.
22. RNA Polymerase I
RNA polymerase I is primarily responsible for synthesis of the major ribosomal RNA precursor in the nucleolus.
Its transcription contributes to production of rRNA components required for ribosome biogenesis.
23. RNA Polymerase III
RNA polymerase III synthesizes several small RNAs, including:
- tRNAs,
- 5S rRNA,
- other small RNA molecules.
24. Promoter Recognition
24.1 Importance
Promoter recognition ensures that transcription begins at the correct location.
The promoter contains DNA elements recognized directly or indirectly by transcription factors.
24.2 Promoter Types
Promoters can contain different combinations of regulatory elements.
Examples include:
- TATA box,
- initiator element,
- downstream promoter element,
- GC-rich elements,
- other promoter-proximal regulatory sequences.
Not every promoter contains all of these elements.
25. Enhancers
25.1 Definition
Enhancers are regulatory DNA sequences that increase transcription of target genes.
They can be located:
- upstream,
- downstream,
- within introns,
- at considerable distances from promoters.
25.2 Mechanism
Activator proteins bind enhancer sequences.
The DNA can form a loop that brings the enhancer-bound proteins into physical proximity with promoter-associated transcription machinery.
This facilitates communication between regulatory regions and the transcription initiation complex.
26. Silencers
Silencers are DNA regulatory elements that reduce transcription.
Repressor proteins bind these sequences and recruit proteins that inhibit transcription.
Silencers can influence gene expression through:
- chromatin compaction,
- inhibition of activators,
- recruitment of corepressors,
- reduction of transcription machinery assembly.
27. Mediator Complex
27.1 Definition
The Mediator is a large multiprotein complex that connects regulatory transcription factors with RNA polymerase II and associated transcription machinery.
27.2 Function
Mediator helps integrate signals from multiple transcription factors.
It can:
- facilitate communication between enhancers and promoters,
- assist RNA polymerase II recruitment,
- regulate transcription initiation,
- coordinate transcription-factor activity.
27.3 Importance
Because multiple activators and repressors can act on the same gene, Mediator provides an important platform for integrating these regulatory signals.
28. Pre-Initiation Complex
28.1 Definition
The pre-initiation complex (PIC) is the assembly of general transcription factors and RNA polymerase II at a promoter before productive transcription begins.
28.2 Formation
A simplified sequence is:
Promoter
↓
TFIID binding
↓
TFIIA and TFIIB recruitment
↓
RNA Polymerase II–TFIIF recruitment
↓
TFIIE recruitment
↓
TFIIH recruitment
↓
Pre-initiation complex
↓
Promoter opening
↓
RNA synthesis
The exact order and dynamics can vary among promoters and cellular contexts.
29. Transcription Initiation Complex
Once the required factors have assembled, the transcription machinery undergoes structural and biochemical changes that allow RNA synthesis to begin.
The DNA around the transcription start site is opened.
The template strand is positioned within the catalytic center of RNA polymerase II.
The first RNA nucleotides are then incorporated.
30. Promoter Clearance
30.1 Definition
Promoter clearance refers to the transition of RNA polymerase from the promoter into productive transcription.
RNA polymerase initially interacts extensively with initiation factors.
After synthesis of an initial RNA segment and appropriate phosphorylation of its CTD, RNA polymerase becomes capable of moving away from the promoter.
30.2 Importance
Promoter clearance marks the transition from transcription initiation to elongation.
31. C-Terminal Domain of RNA Polymerase II
31.1 Structure
RNA polymerase II contains a C-terminal domain, commonly abbreviated CTD, on its largest subunit.
The CTD contains repeated peptide sequences.
31.2 Functional Importance
The CTD acts as a dynamic platform for recruitment of factors involved in:
- transcription,
- RNA capping,
- RNA splicing,
- 3′ end processing,
- transcription termination.
Different phosphorylation states of the CTD are associated with different stages of the transcription cycle.
32. Transcription Elongation Machinery
After promoter clearance, RNA polymerase II enters the elongation phase.
Several elongation factors regulate polymerase movement and RNA synthesis.
They can influence:
- polymerase processivity,
- pausing,
- transcriptional speed,
- nucleosome traversal,
- RNA processing.
33. RNA Polymerase Pausing
RNA polymerase II can pause shortly after transcription begins.
This pausing provides an additional regulatory checkpoint.
The cell can control whether paused polymerase:
- remains paused,
- enters productive elongation,
- undergoes termination.
This mechanism is especially important for genes that need rapid activation in response to signals.
34. Chromatin and Transcription Machinery
34.1 Nucleosomes as Barriers
Eukaryotic DNA is wrapped around histone proteins to form nucleosomes.
Because nucleosomes restrict DNA accessibility, transcription machinery must interact with chromatin rather than naked DNA.
34.2 Chromatin Remodeling
ATP-dependent chromatin-remodeling complexes can reposition or restructure nucleosomes.
This can expose promoter or enhancer sequences to transcription factors.
34.3 Histone Modifications
Histones can be chemically modified.
Important modifications include:
- acetylation,
- methylation,
- phosphorylation,
- ubiquitination.
These modifications influence recruitment and activity of transcription-associated proteins.
35. Histone Acetylation and Transcription
Histone acetylation is frequently associated with transcriptionally active chromatin.
Histone acetyltransferases add acetyl groups to histones.
This can reduce certain histone-DNA interactions and create binding sites for proteins that promote transcription.
Histone deacetylases remove these acetyl groups and often contribute to transcriptional repression.
36. DNA Methylation and Transcription
DNA methylation can influence transcription by modifying DNA and recruiting proteins that recognize methylated DNA.
In many promoter contexts, increased DNA methylation is associated with transcriptional repression.
However, the effect of methylation depends on its location and genomic context.
37. Coactivators
37.1 Definition
Coactivators are regulatory proteins or complexes that increase transcription but often do not directly recognize DNA sequences.
37.2 Functions
Coactivators may:
- recruit RNA polymerase machinery,
- recruit Mediator,
- modify histones,
- remodel chromatin,
- stabilize activator-promoter interactions.
38. Corepressors
Corepressors are proteins or complexes that assist transcriptional repression.
They may recruit:
- histone deacetylases,
- chromatin-remodeling factors,
- DNA methylation-associated proteins,
- other repressive complexes.
Thus, corepressors convert transcription-factor binding into a broader inhibitory chromatin environment.
39. DNA Looping
Enhancers and promoters may be separated by large stretches of DNA.
DNA looping brings these regions into functional proximity.
A simplified mechanism is:
Activator binds enhancer
↓
DNA looping
↓
Enhancer approaches promoter
↓
Mediator/coactivator interactions
↓
Transcription machinery recruitment
↓
Increased transcription
40. Combinatorial Control
One of the most important principles of eukaryotic transcription regulation is combinatorial control.
A gene is often regulated not by one transcription factor but by a combination of several factors.
For example:
Activator A + Activator B + Chromatin regulator + Mediator
may be required for strong expression.
Another combination may repress the same gene.
This allows a relatively limited number of regulatory proteins to generate highly diverse gene-expression patterns.
41. Transcription Factor Dimerization
Many transcription factors function as dimers.
Dimerization can:
- stabilize DNA binding,
- alter DNA sequence specificity,
- recruit different regulatory proteins,
- generate different transcriptional responses.
Homodimers contain two identical proteins, whereas heterodimers contain different proteins.
42. Regulation by Post-Translational Modification
Transcription factors can be activated or inhibited through chemical modifications.
Important modifications include:
- phosphorylation,
- acetylation,
- methylation,
- ubiquitination,
- sumoylation.
These modifications can alter:
- DNA-binding ability,
- nuclear localization,
- protein stability,
- interaction with coactivators,
- interaction with corepressors.
43. Nuclear Localization of Transcription Factors
Many transcription factors must enter the nucleus to interact with DNA.
Cellular signals can control their nuclear localization.
For example:
Signal
↓
Protein modification
↓
Exposure of nuclear localization signal
↓
Nuclear import
↓
DNA binding
↓
Gene regulation
This provides a rapid mechanism for converting external signals into transcriptional responses.
44. Hormone Receptors as Transcription Factors
Some hormones, particularly steroid hormones, can enter cells and bind intracellular receptors.
The hormone-receptor complex can act as a transcription factor.
The activated receptor binds specific DNA regulatory elements and recruits coactivators or corepressors.
This provides a direct link between hormone signaling and gene expression.
45. Transcription Machinery in Bacteria
Bacterial transcription machinery is generally simpler than the eukaryotic system.
The core RNA polymerase associates with a sigma factor to recognize promoter sequences.
45.1 Bacterial RNA Polymerase
The core enzyme contains multiple subunits, commonly represented as:
α₂ββ′ω
45.2 Sigma Factor
Sigma factor determines promoter-recognition specificity.
Different sigma factors allow RNA polymerase to recognize different groups of genes.
This enables bacteria to rapidly change gene expression in response to environmental conditions.
46. Bacterial Transcription Factors
Bacterial transcription is regulated by:
- activators,
- repressors,
- sigma factors,
- small regulatory molecules,
- DNA-binding regulatory proteins.
These factors can influence RNA polymerase binding and promoter activity.
47. Operator and Regulatory DNA
In many bacterial systems, transcription factors bind DNA regions called operators or other regulatory elements.
A repressor bound to an operator can prevent productive transcription.
An activator can increase transcription by helping RNA polymerase bind or function efficiently at the promoter.
48. Operons
An operon is a genetic regulatory unit in bacteria in which multiple related genes can be controlled by a common promoter and regulatory region.
Examples include:
- lac operon,
- trp operon.
Operons allow bacteria to coordinate expression of genes involved in the same metabolic pathway.
49. Transcription Machinery and RNA Processing
In eukaryotes, transcription machinery is closely connected with RNA-processing machinery.
As RNA polymerase II synthesizes RNA, processing factors can be recruited to the CTD.
This coordinates:
- 5′ capping,
- splicing,
- 3′ end processing,
- transcription termination.
Thus, transcription is not an isolated event but part of a larger gene-expression process.
50. Transcription and Gene Expression
Transcription factors and machinery determine which genes produce RNA.
The amount and timing of transcription influence downstream protein production.
Therefore:
Transcription factor activity → transcription rate → RNA abundance → protein production → cellular function
This relationship explains why transcriptional regulation is central to cell biology.
51. Regulation During Development
During development, transcription factors establish specific gene-expression programs.
A transcription factor activated in one developing tissue may activate one set of genes, whereas another combination of transcription factors in a different tissue may activate a different set.
This process contributes to:
- cell differentiation,
- tissue specification,
- organ development,
- maintenance of cell identity.
52. Transcription Factors in Cell Differentiation
Differentiation requires coordinated activation and repression of thousands of genes.
Transcription factors form regulatory networks in which:
- one factor activates another,
- several factors cooperate,
- some factors repress alternative cell fates.
These networks establish stable patterns of gene expression.
53. Transcriptional Regulatory Networks
A transcriptional regulatory network consists of interacting transcription factors and target genes.
A simplified network may look like:
TF-A → activates Gene B
TF-B → activates Gene C
TF-C → represses Gene D
TF-A + TF-C → regulate Gene E
Such networks allow cells to integrate multiple signals and produce coordinated responses.
54. Transcription Factors and Environmental Response
Environmental conditions can rapidly change transcription-factor activity.
Examples include:
- heat stress,
- oxidative stress,
- nutrient limitation,
- DNA damage,
- osmotic stress,
- inflammatory signals.
Activated transcription factors induce expression of genes that help the cell adapt.
55. Transcription Factor Specificity
The specificity of a transcription factor depends on several properties:
- DNA-binding sequence,
- concentration,
- interaction partners,
- chromatin accessibility,
- post-translational modifications,
- cellular location.
Therefore, DNA binding alone does not always determine whether a gene will be expressed.
56. Combinatorial Transcriptional Regulation
A gene may contain multiple regulatory regions.
Different transcription factors can bind these regions simultaneously.
The final transcriptional outcome depends on the combined effects of:
- activators,
- repressors,
- chromatin regulators,
- Mediator,
- general transcription factors.
This principle allows precise and context-dependent control of gene expression.
57. Transcription Factor Competition
Different transcription factors may compete for overlapping or nearby DNA-binding sites.
Competition can determine whether a gene is activated or repressed.
For example:
Activator binding → transcription increases
Repressor binding → transcription decreases
The relative abundance and activity of the factors can determine the final outcome.
58. Pioneer Factors and Chromatin Accessibility
Some transcription factors can bind relatively inaccessible DNA and initiate chromatin changes.
These factors can facilitate subsequent recruitment of other transcription factors.
This provides a mechanism through which transcriptional programs can be established during differentiation and development.
59. Transcriptional Memory
Some cells can maintain altered gene-expression states after the initial signal has disappeared.
This can occur through:
- persistent transcription-factor networks,
- chromatin modifications,
- DNA methylation,
- stable regulatory complexes.
Such mechanisms contribute to cellular identity and long-term gene-expression patterns.
60. Transcription Machinery: Integrated Mechanism
The complete process can be summarized as:
1. Regulatory signal
↓
2. Transcription-factor activation
↓
3. Binding to regulatory DNA
↓
4. Chromatin remodeling
↓
5. Enhancer-promoter communication
↓
6. Mediator recruitment
↓
7. General transcription-factor assembly
↓
8. RNA polymerase II recruitment
↓
9. Pre-initiation complex formation
↓
10. DNA opening
↓
11. RNA synthesis initiation
↓
12. Promoter clearance
↓
13. Elongation
↓
14. RNA processing
↓
15. Termination
↓
16. Mature RNA
61. Comparison of General and Sequence-Specific Transcription Factors
| Feature | General Transcription Factors | Sequence-Specific Transcription Factors |
|---|---|---|
| Main role | Core transcription initiation | Gene-specific regulation |
| Requirement | Required for transcription by the relevant polymerase | Required only for selected genes |
| DNA recognition | Often recognize promoter/core elements indirectly or directly | Recognize specific regulatory DNA sequences |
| Examples | TFIID, TFIIB, TFIIE, TFIIH | Steroid receptors, developmental TFs, activators, repressors |
| Main function | Assemble transcription machinery | Activate or repress selected genes |
| Specificity | Broad | High |
| Major location | Promoter/core transcription machinery | Promoters, enhancers, silencers and other regulatory regions |
62. Comparison of Activators and Repressors
| Feature | Activators | Repressors |
|---|---|---|
| Effect | Increase transcription | Decrease transcription |
| DNA binding | Promoter/enhancer/regulatory regions | Silencers or other regulatory regions |
| Recruitment | Coactivators and transcription machinery | Corepressors and repressive complexes |
| Chromatin effect | Often promotes accessibility | Often promotes reduced accessibility |
| RNA polymerase | Facilitates recruitment/activity | Can inhibit recruitment/activity |
63. Important Molecular Interactions
Transcription depends on extensive protein-protein and protein-DNA interactions.
Important interactions include:
Transcription factor ↔ DNA
Transcription factor ↔ Mediator
Mediator ↔ RNA polymerase II
General transcription factor ↔ promoter
Chromatin remodeler ↔ nucleosome
Histone modifier ↔ histone
Elongation factor ↔ RNA polymerase II
These interactions create a dynamic transcriptional system.
64. Biological Significance
Transcription factors and machinery are essential for:
64.1 Gene Expression
They determine whether genes are expressed.
64.2 Cell Differentiation
They establish cell-specific gene-expression programs.
64.3 Development
They regulate developmental pathways and tissue formation.
64.4 Environmental Adaptation
They allow cells to respond to changes in their environment.
64.5 Cellular Homeostasis
They maintain appropriate levels of proteins and RNAs.
64.6 DNA Damage Response
Some transcription factors activate genes involved in DNA repair and stress responses.
64.7 Metabolism
Transcriptional regulation coordinates enzymes and transporters involved in metabolic pathways.
65. Abnormal Transcription Factor Activity
Because transcription factors regulate many genes, abnormal activity can have broad consequences.
Changes in transcription-factor function can result from:
- mutation,
- altered expression,
- abnormal signaling,
- defective protein modification,
- altered DNA binding,
- changes in chromatin accessibility.
These changes can disrupt normal cellular programs and contribute to developmental abnormalities and disease processes.
