Which phenotype would you expect to have the higher mutation

Which phenotype would you expect to have the higher mutation rate, rifampin resistance or Arg auxotrophy (Arg-). Rifampin inhibits transcription by binding to RNA polymerase, and RifR mutations change the RNA polymerase so that it no longer binds rifampin but still functions to make RNA.

Solution

Ans: Rifampin resistance phenotype will have higher mutational rate when compared to Arg auxotrophy (Arg-).

Rifampin inhibits transcription by binding to RNA polymerase, and RifR mutations change the RNA polymerase so that it no longer binds rifampin but still functions to make RNA. It alters the rifampin binding site on RNA polymerase, which results in the decreased affinity for rifampicin. Rifampin resistance mutations lead to a temperature-sensitive phenotype in E. coli.

When transport activity was examined in strains with mutations leading to derepression of arginine biosynthesis, the regulation of arginine transport was found to be normal. Canavanine is a toxic arginine analog, whose uptake requires the arginine transporter. Canavanine selects for loss-of-function mutants of this transporter, which is encoded by the CAN1 gene.