Run-off transcription is an in vitro biochemical assay designed to study promoter strength and transcription factor requirements. A DNA template containing a promoter followed by a defined sequence is linearized downstream with restriction enzymes, causing RNA polymerase to transcribe and then fall off at the cut site, producing a transcript of fixed length. Reactions include labeled UTP and nuclear extracts or purified factors. Quantity of RNA synthesized is measured by autoradiography. Northern blot detects steady-state RNA, SAGE quantifies tags, and ChIP assesses protein occupancy, not tran
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NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.