Attenuation of trp operon transcription is controlled by the formation of stem-loop structures in mRNA. The attenuation function can be disrupted by mutations that alter the sequence of repeat DNA regions 1 to 4 and prevent the formation of mRNA stem loops. Describe the likely effects on attenuation of each of the following mutations under the conditions specified.

Consider the transcription of genes of the lac operon under two conditions: (1) when both glucose and lactose are present and (2) when glucose is absent and lactose is present. Describe the comparative levels of transcription of lac operon genes under these conditions, and explain the molecular basis for the difference.

Define antisense RNA, and describe how it affects the translation of a complementary mRNA. Why is it more advantageous to the organism to stop translation initiation than to inactivate or destroy the gene product after it is produced?

Describe the lytic and lysogenic life cycles of λ bacteriophage. What roles do λ repressor and Cro protein play in controlling transcription from P_R and P_RM, and how are these roles linked to lysis and lysogeny?

In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?

Mutation of consensus sequence in the lac promoter

In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?

Mutation of the repressor binding site on the operator sequence

In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?

Mutation of the lacI gene affecting the allosteric site of the protein