Final answer:
A mutation in the sigma subunit would likely result in impaired transcription initiation, potentially leading to a decrease in gene expression and affecting the cell's ability to respond to environmental stimuli.
Step-by-step explanation:
If a specific sigma subunit were mutated, the likely result would be impaired transcription initiation in bacterial cells, as the sigma subunit is responsible for guiding RNA polymerase to the correct initiation sites on DNA. Sigma factors are key components of bacterial RNA polymerase that recognize and bind to specific promoter regions of DNA. A mutation in the sigma subunit could lead to decreased affinity for promoters, resulting in reduced transcription of essential genes.
Depending on the nature of the mutation, the consequences could range from mild to severe, potentially affecting the cell's ability to respond to environmental changes and regulation of gene expression. If the mutation prevented sigma from releasing properly after initiation, it could also cause transcription elongation issues.