In B lichenformis a few amino acids are removed from the Cte

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

A) What was the mutational event that gave rise to the frameshift mutant ?

Solution

ADDITION is the mutational event responsible for this frameshift

A frameshift mutation is a genetic mutation which results due to insertions or deletions of a number of nucleotides in a provided DNA sequence which is not divisible by three.

Wild-type: N M N G K (Asn-Met-Asn-Gly-Lys)

Mutant: N M I W Q I C V M K D (Asn-Met-Ileu-Trp-Gln-Ileu-Cys-Val-Met-Lys-Asp)

Here the change has occurred from third base i.e N onwards

N is encoded by AAT or AAC

I is encoded by ATT or ATC or ATA

Based on the above information we can say, incase, of AAT, after the A, T base has been added resulting in frameshift mutation.

wildtype:

AAT ATG AAT GGC AAA

N.........M…..N…...G…...K...

mutant:

AAT ATG ATA TGG CAA

N…....M.......I…...W….Q...I...C...V...M...K...D