Question

Acridine dyes such as proflavin are known to induce primarily single base-pair additions and deletions. Suppose that the wild-type nucleotide sequence in the mRNA produced from a gene is 5'-AUGCCCUUUGGGAAAGGGUUUCCCUAA-3' Also, assume that a mutation is induced within this gene by proflavin and, subsequently, a revertant of this mutation is similarly induced with proflavin and shown to result from a second-site suppressor mutation within the same gene. If the amino acid sequence of the polypeptide encoded by this gene in the revertant (double mutant) strain is NH2-Met-Pro-Phe-Gly-Glu-Arg-Phe-Pro-COOH What would be the most likely nucleotide sequence in the mRNA of this gene in the revertant (double mutant)? Be very clear and specific...brief answers will receive little to no credit. You must show and explain all work to receive credit.

Answer 1

WT mRNA sequence = 5'-AUG CCC UUU GGG AAA GGG UUU CCC UAA-3'
WT protein sequence = NH2-Met-Pro-Phe-Gly-Lys-Gly-Phe-Pro-COOH
Double mutant (Revertant) sequence = NH2-Met-Pro-Phe-Gly-Glu-Arg-Phe-Pro-COOH

The revertant contains two amino acid changes compared to the WT sequence.

The mutant protein sequence could be = NH2-Met-Pro-Phe-Gly-Glu-Gly-Phe-Pro-COOH
It contains an acidic amino acid in the place of a basic amino acid.
So, Lys is mutated to Glu.
Lys codon in the WT sequence = AAA
Codon for Glu = GAA
So, there is an A to G transition.
Mutant mRNA sequence = 5'-AUG CCC UUU GGG GAA GGG UUU CCC UAA-3'

The revertant contains Arg in the place of Gly.
So, Gly is mutated to Arg.
Gly codon in the WT sequence = GGG
Codon for Arg = AGG
So, there is a G to A transition.
Revertant mRNA sequence = 5'-AUG CCC UUU GGG GAA AGG UUU CCC UAA-3'