Q.The RNA polymerase holoenzyme transcribes:
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Start your 14-day free trial to unlock the full solution →The RNA polymerase holoenzyme transcribes only the structural gene and the terminator region — not the promoter itself.
The question touches on a fundamental point about how transcription works in bacteria, and it often trips students up because of a simple confusion: what the enzyme binds to versus what it copies.
In the lac operon — and indeed in any bacterial transcription unit — the RNA polymerase holoenzyme first recognises and binds to the promoter region. That binding is essential; without it, transcription cannot start. But binding is not the same as transcribing. The promoter is a DNA sequence that serves as a docking site, not a template for RNA synthesis. The enzyme does not make an RNA copy of the promoter itself.
Once bound, the holoenzyme unwinds the DNA and begins moving along the template strand, synthesising RNA complementary to the structural gene (or genes, in an operon). It continues until it reaches the terminator region, where a specific sequence signals the enzyme to stop and release the RNA transcript. So the actual RNA product includes the sequence of the structural gene(s) and the terminator region — but never the promoter.
In some contexts, the term "transcribes" might be loosely used to mean "copies into RNA". The promoter is never copied; it is only recognised and bound. …
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