Question

Which one of the following \(\sigma\) (sigma) factors is responsible for the transcriptional regulation of nitrogen assimilation?

• A. \(\sigma 70\)
• B. \(\sigma 54\)
• C. \(\sigma 28\)
• D. \(\sigma 24\)

Hint:

\(\sigma 54\) is also called nitrogen sigma factor because it regulates genes involved in nitrogen fixation and assimilation.

Answer 1

The Correct Option is B

Step 1: Understand sigma factors.
Sigma (\(\sigma\)) factors are protein subunits of bacterial RNA polymerase that help recognize specific promoter sequences and initiate transcription. Different sigma factors regulate different groups of genes.

Step 2: Identify the role of \(\sigma 70\).
\(\sigma 70\) is the primary housekeeping sigma factor in bacteria and is mainly involved in transcription of essential genes required for normal growth. Therefore, it is not specifically associated with nitrogen assimilation.

Step 3: Identify the role of \(\sigma 54\).
\(\sigma 54\), also called \(\sigma^N\), is specifically involved in the regulation of genes related to nitrogen metabolism and nitrogen assimilation in bacteria.

Step 4: Analyze \(\sigma 28\).
\(\sigma 28\) is mainly associated with the regulation of genes involved in flagellar synthesis and motility. Hence, it is not related to nitrogen assimilation.

Step 5: Analyze \(\sigma 24\).
\(\sigma 24\) generally participates in extracytoplasmic stress responses and envelope stress regulation. Thus, it is not responsible for nitrogen assimilation.

Step 6: Compare all the sigma factors.
Among the given sigma factors, only \(\sigma 54\) specifically regulates transcription of genes involved in nitrogen fixation and nitrogen assimilation pathways.

Step 7: Final conclusion.
Therefore, the sigma factor responsible for transcriptional regulation of nitrogen assimilation is
\[ \boxed{\sigma 54} \]
Hence, the correct answer is option (B).