Final answer:
Sigma plays a crucial role in the regulation of gene expression by guiding RNA polymerase to specific DNA sequences called promoter regions.
Step-by-step explanation:
Sigma plays a crucial role in the regulation of gene expression in prokaryotes. Sigma factors are proteins that bind to RNA polymerase and guide it to specific DNA sequences called promoter regions. These promoter regions are located upstream of genes and determine where and when transcription initiates.
By binding to different sigma factors, RNA polymerase can recognize different promoter sequences and transcribe different sets of genes. This allows the cell to respond to changing environmental conditions or internal signals by selectively transcribing specific genes.
For example, in the bacterium E. coli, there are multiple sigma factors that recognize different promoter sequences and regulate the expression of genes involved in stress response, nutrient utilization, and other cellular processes.