What would explain a mutation in a strain of bacteria?

Question

The strain has x amount of an enzyme, but a mutant detived from that strain has 1.53 of the enzyme. There is no change in the coding region of the gene. But there is a subtitution of two A-T base pairs in the mutant for two G-C base pairs where polymerase attaches. What would explain how a mutation could produce this change in protein level and what change would occur in mRNA level?

Answer 1

Bacterial RNA polymerase has a sigma subunit that is able to recognize the promoter region upstream of the structural gene. This region is often referred to as the TATA box. A change in the sequence affects the affinity of polymerase to bind to the promoter. Because I am not sure about what you mean by “1.53 of the enzyme” I will give it to you both ways. A change in the promoter could reduce the affinity of RNA polymerase, this will in turn reduce the amount of times the polymerase will association with the promoter. And therefore reduce transcription and ultimately translation of the RNA into a functional enzyme. This type of mutation is known as a “down mutation”. The other way is basically the reverse of this situation; the mutation is this case increase the affinity of the promoter for polymerase, which therefore increases association, translation and gene expression. This situation is quite fittingly called an “up mutation”.

Hope this help

Answer 2

The mutations affect the promoter region of the gene, making it more effective at using RNA polymerase (the GC to AT mutations could allow for easier access to the template strand by decreased hydrogen bonding). This results in increased transcription of the gene, leading to increased enzyme production.