You have studied mutations in a transcription regulatory protein from Bacillus subtilis by an in vivo reporter gene assay carried out in Escherichia coli. The cis-regulatory sequence that the protein normally recognizes was inserted upstream of a gene encoding an enzyme that can produce a visible blue product.
A) Their colonies turn blue at permissive (low) temperatures.
B) Their colonies turn blue at permissive (high) temperatures.
C) Their colonies turn blue at nonpermissive (low) temperatures.
D) Their colonies turn blue at nonpermissive (high) temperatures.
E) coli cells were then transformed with the reporter construct along with the gene encoding one of the various mutant forms of the transcription regulatory protein. Since the transcription regulatory protein is an inhibitor, the colonies turn blue only when the mutant protein is nonfunctional and unable to inhibit gene expression. Interestingly, you have identified a number of "cold-sensitive" loss-of-function mutations that show the mutant phenotype at 22°C but not at 37°C. Which of the following correctly describes the phenotype of these cold-sensitive mutants?

Question

Quizplus · Accepted Answer

As long as the permissive conditions prevail, conditional mutants function normally. In this example, only under nonpermissive conditions (i.e. at low temperatures) do the mutations abort the inhibitory function of the protein, resulting in blue colonies.

You Have Studied Mutations in a Transcription Regulatory Protein from Bacillus