Regulation of Gene Expression in Prokaryotes (1B) Practice Test

A bacterium regulates an amino acid transporter operon via an inducible repressor that dissociates from DNA when bound by the transported amino acid. Cells were grown without the amino acid, then 1 mM amino acid was added. Transporter mRNA increased within 5 minutes.

Which observation is most consistent with the regulatory mechanism described?

Investigators compare two bacterial genes regulated by different sigma factors. Gene H is transcribed by RNA polymerase containing $\sigma^{70}$ under nutrient-rich conditions. Gene S is transcribed by RNA polymerase containing $\sigma^{S}$ during stationary phase. In a strain with a loss-of-function mutation in $\sigma^{S}$, cultures are grown to stationary phase and mRNA levels are measured relative to wild-type stationary phase.

Based on the scenario, which outcome would be expected given the gene regulation process?