RNA polymerase in a prokaryote is composed of several subunits. Most of these subunits are the same for the transcription of any gene, but one, known as sigma, varies considerably. Which of the following is the most probable advantage for the organism of such variability in RNA polymerase?

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The variability in the sigma subunit allows the RNA polymerase to recognize different promoters under certain environmental conditions. This allows the organism to regulate which genes are transcribed and at what levels in response to changes in the environment. For example, a bacterium may need to express certain genes only when a specific nutrient is available, and the variability in sigma allows the RNA polymerase to selectively transcribe those genes in response to that nutrient.

RNA Polymerase in a Prokaryote Is Composed of Several Subunits