In B. lichenformis a few amino acids are removed from the C-terminal end of the
ID: 188176 • Letter: I
Question
In B. lichenformis a few amino acids are removed from the C-terminal end of the beta-lactamase enzyme after it is synthesized. The sequence of the original C-terminus can be deduced by comparing it to a mutant in which the reading frame is shifted by insertion or deletion of a nucleotide. the amino acid sequence of the purified wild-type enzyme and the frameshift mutant from amino acid 263 to the C-terminus are given below.
Wild-type: N M N G K
Mutant: N M I W Q I C V M K D
1. What was the mutational event that gave rise to the frameshift mutation?
2. Deduce the number of amino acids in the synthesized (pro-enzyme) from the wild-type enzyme and, as far as possible, the actual sequence of the wild-type enzyme.
Explanation / Answer
wild type - NMNGK
CODON SEQUENCE - AAU AUG AAU GGC AAA
MUTANT - NMIWQCVMKD
CODON SEQUENCE - AAU AUG AUA UGG CAA AUA UGU GUA AUG AAA GAU
in the mutant insertion of U nucleotide shifted the frame. if the U (underlined and bold) was not inserted then the wild-type sequence will be -
NMNGKYV#(STOP CODON) = 269 AMINO ACID LONG WILD TYPE PROTEIN.
CODON SEQUENCE - AAU AUG AAU GGC AAA UAU GUG UAA