I was asked the following question by my teacher:
A gene regulatory protein called HisP regulates the enzymes for histidine biosynthesis in the bacterium E. Coli. HisP is a protein whoes activity is modulated by histidine. Upon binding histidine, HisP alters its conformation, dramatically changing its affinity for the regulatory sequences in the promoters of the genes for the histidine biosynthetic enzymes.
If HisP function sas a transcriptional repressor, would you expect that HisP would bind more tightly or less tightly to regulatory sequences when histidine is abundant? Why?
My own attempt at a solution:
Less tightly. If histidine is abundant, HisP's job is to stop the histadine pathway as a "repressor." If HisP binds less tightly to promotors, the pathway should not produce as much histadine.