A mutation of a sigma factor in a bacterium would most likely affect the:

• A. initiation of transcription
• B. translation of mRNA
• C. replication of DNA
• D. synthesis of ribosomal RNA

Answer: (A)

Verified step by step guidance

1. Understand the role of sigma factors in bacteria: Sigma factors are proteins that bind to RNA polymerase and direct it to specific promoter regions on the DNA to initiate transcription.
2. Recall that transcription is the process where RNA polymerase synthesizes RNA from a DNA template, and sigma factors are essential for recognizing the start sites of genes.
3. Consider what would happen if a mutation occurred in a sigma factor: it would likely impair the ability of RNA polymerase to correctly initiate transcription at the promoter regions.
4. Evaluate the other options: translation of mRNA involves ribosomes and tRNAs, replication of DNA involves DNA polymerase, and synthesis of ribosomal RNA is a subset of transcription but still depends on initiation by RNA polymerase and sigma factors.
5. Conclude that a mutation in a sigma factor most directly affects the initiation of transcription, as sigma factors are specifically involved in guiding RNA polymerase to start transcription.