Q.98 The expression of a gene is regulated by a transcription factor. Which of the
following techniques can be used to identify the region in its promoter where the
transcription factor binds?
(A) S1 nuclease mapping
(B) Chromatin immunoprecipitation followed by sequencing
(C) Electrophoretic mobility shift assay
(D) DNase I footprinting

DNase I footprinting precisely identifies transcription factor binding regions in gene promoters by revealing protected DNA sequences. Both Chromatin immunoprecipitation followed by sequencing (ChIP-seq) and Electrophoretic mobility shift assay (EMSA) detect binding but lack exact site localization within promoters. S1 nuclease mapping maps transcript ends instead.

Correct Answer

(D) DNase I footprinting

This technique directly visualizes the specific nucleotide region in the promoter protected from DNase I digestion by the bound transcription factor, providing high-resolution mapping.

Option Analysis

(A) S1 Nuclease Mapping

S1 nuclease mapping identifies 5′ and 3′ ends of RNA transcripts by hybridizing labeled DNA probes to RNA and digesting unpaired regions. It maps transcription start sites or intron positions but cannot detect transcription factor binding sites in promoters, as it focuses on RNA-DNA hybrids rather than protein-DNA interactions.

(B) Chromatin Immunoprecipitation Followed by Sequencing (ChIP-seq)

ChIP-seq pulls down transcription factor-bound chromatin using specific antibodies, then sequences DNA to map genome-wide binding locations. While powerful for identifying promoter enrichment, it shows binding regions (peaks) spanning hundreds of base pairs but requires additional steps like motif analysis for exact site identification, lacking single-nucleotide precision in promoters.

(C) Electrophoretic Mobility Shift Assay (EMSA)

EMSA detects protein-DNA binding by observing slower migration of labeled DNA probes forming complexes with transcription factors in native gels. It confirms interaction and specificity using mutated probes or competitors but reveals no sequence information about the binding region within the promoter.

(D) DNase I Footprinting

DNase I footprinting incubates labeled promoter DNA with the transcription factor, performs partial DNase I digestion, and runs products on denaturing gels. Bound regions appear as “footprints” (gaps) where cleavage is blocked, precisely mapping the binding site at nucleotide resolution.

Introduction to Transcription Factor Promoter Binding

Transcription factor binding site identification is crucial for understanding gene regulation in molecular biology. Techniques like DNase I footprinting precisely map where transcription factors bind promoter regions, essential for CSIR NET Life Sciences preparation.

This article breaks down four key methods, highlighting why DNase I footprinting excels for promoter-specific analysis.

DNase I Footprinting: Gold Standard for Precise Mapping

DNase I footprinting uses end-labeled promoter DNA fragments incubated with transcription factors. Limited DNase I digestion cuts accessible DNA, but bound sites resist cleavage, creating visible footprints on sequencing gels.

• Offers nucleotide-level resolution for exact binding coordinates

• Ideal for validating computational predictions in vitro

• Widely used for promoter architecture studies

ChIP-seq: Genome-Wide Binding Detection

Chromatin immunoprecipitation followed by sequencing (ChIP-seq) crosslinks proteins to DNA, immunoprecipitates with TF antibodies, and sequences enriched fragments. It maps thousands of binding sites but peaks cover ~200-500 bp, needing follow-up for precise motifs.

EMSA: Confirming Specific Interactions

Electrophoretic mobility shift assay mixes labeled promoter probes with TFs, observing gel shifts from complexes. Competition with mutants confirms specificity but identifies no binding sequence details.

S1 Nuclease Mapping Limitations

S1 nuclease mapping hybridizes probes to RNA for transcript end mapping via single-strand digestion. It locates start sites indirectly but ignores protein binding entirely.

CSIR NET Exam Insights

For competitive exams, recognize DNase I footprinting’s direct promoter visualization versus ChIP-seq’s broad profiling or EMSA’s qualitative shifts. Practice distinguishing in vitro precision from in vivo mapping.