Question

In the lab, you isolate a mutant strain of bacteria in which the phosphatase that would normally dephosphorylate NtrC-P is defective. Assuming the levels of NtrB and NtrC protein remain normal (same as wild type), what is the expected phenotype of this mutant

Answer 1

GlnA will be overexpressed and the cells will have more glutamine than glutamate

Step-by-step explanation:

Glutamine synthetase (glnA) is an enzyme involved in nitrogen metabolism that catalyzes the amidation of glutamate to glutamine. Moreover, the phosphorylated form of the NtrC response regulator protein (NtrC~P) acts as a transcriptional activator of genes associated with nitrogen metabolism, including glnA. NtrC~P exhibits 1-an enhanced DNA binding activity (increased oligomerization on the target DNA template) and 2-ATPase activity (oligomerization of the NtrC phosphoprotein), which are fundamental features for transcriptional activation. In consequence, it is expected that a higher level of NtrC~P (due to a defective form of the phosphatase that dephosphorylates NtrC~P) leads to the overexpression of glnA, thereby increasing glutamine levels and simultaneously decreasing glutamate concentration.