In a particular bacterial species, temperature-sensitive conditional mutations cause expression of a wild-type phenotype at one growth temperature and a mutant phenotype at another—typically higher—temperature. Imagine that when a bacterial cell carrying such a mutation is shifted from low to high growth temperatures, RNA polymerases in the process of elongation complete transcription normally, but no new transcripts can be started. The mutation in this strain most likely affects: a. the terminator sequence b. the start codon c. sigma d. one of the polypeptides of the core RNA polymerase

Key Concepts

RNA Polymerase Function

RNA polymerase is an enzyme responsible for synthesizing RNA from a DNA template during transcription. It binds to the promoter region of a gene to initiate transcription and elongates the RNA strand by adding nucleotides complementary to the DNA template. Understanding its role is crucial for analyzing how mutations can affect transcription initiation and elongation.

Transcription Initiation

Transcription initiation is the process where RNA polymerase binds to the promoter region of a gene, requiring specific sequences and factors, such as sigma factors in bacteria. If a mutation affects the components necessary for this step, it can lead to the inability to start new transcripts, even if elongation of existing transcripts occurs normally.

Conditional Mutations

Conditional mutations are genetic alterations that result in a phenotype that is only expressed under certain environmental conditions, such as temperature. In this scenario, the mutation allows for normal function at lower temperatures but disrupts transcription initiation at higher temperatures, highlighting the relationship between genetic expression and environmental factors.