Final answer:
Mutation of a specific sigma subunit of RNA polymerase would most likely cause RNA polymerase to fail to initiate transcription at the promoter specific to the sigma subunit, as this subunit is essential for recognizing the correct starting point for transcription.
Step-by-step explanation:
Impact of a Sigma Subunit Mutation
If a specific sigma subunit of RNA polymerase were mutated, the result would likely be that RNA polymerase would fail to initiate transcription at the promoter specific to the sigma subunit. The sigma subunit of prokaryotic RNA polymerase is crucial for the initiation of transcription as it recognizes promoter sequences on the DNA and facilitates the binding of the RNA polymerase holoenzyme to the start of a gene. If the sigma subunit is mutated, the altered recognition function may result in the inability of the RNA polymerase to accurately locate and bind to the promoter, therefore hindering the initiation of transcription and potentially leading to the failure of gene expression.
It is important to note that the sigma subunit does not affect the stability of the core enzyme, as it only participates in the transcription initiation stage. Therefore, other outcomes like destabilization of the core enzyme or failed elongation of RNA are not primary consequences of sigma subunit mutations. Mutation of the sigma subunit affects transcription initiation specificity but has no direct effect on RNA polymerase’s ability to elongate a transcript once initiated.