Q.37 Which of the following is/are involved in the initiation of DNA replication?
(A) RhoA (B) oriC
(C) Sigma factor (D) DnaA
DNA Replication Initiation: Correct Answer to MCQ Q.37 with oriC and DnaA Explained
DNA replication initiation in bacteria involves specific proteins and sequences at the origin. The correct answers are (B) oriC and (D) DnaA.
Correct Answer
Options (B) oriC and (D) DnaA are involved in initiating bacterial DNA replication. oriC serves as the origin of replication site, while DnaA acts as the key initiator protein that binds to oriC to trigger the process.
oriC Role
oriC is the chromosomal origin of replication in bacteria like E. coli, containing DnaA-binding boxes and AT-rich regions. DnaA proteins bind these boxes, forming a complex that unwinds the DNA duplex at the AT-rich due to torsional stress, enabling helicase loading.
DnaA Function
DnaA, an AAA+ ATPase, exists in ATP-bound active form that preferentially binds low-affinity sites in oriC. It oligomerizes to melt DNA strands and recruits DnaB helicase and DnaC for replication fork assembly, ensuring once-per-cell-cycle initiation.
RhoA Explanation
RhoA is a eukaryotic GTPase involved in actin cytoskeleton regulation and cell signaling, not DNA replication. It plays no role in bacterial or prokaryotic replication initiation.
Sigma Factor Details
Sigma factor is a prokaryotic transcription initiation subunit of RNA polymerase, aiding promoter recognition on DNA. It functions in RNA synthesis, unrelated to DNA replication.
| Option | Role | Involved in DNA Replication Initiation? |
|---|---|---|
| (A) RhoA | Eukaryotic | No |
| (B) oriC | Bacterial replication origin | Yes |
| (C) Sigma factor | Transcription initiation | No |
| (D) DnaA | Initiator protein binds oriC | Yes |
