A few amino acids are post-translationally removed from the C-terminal end of th

Question

A few amino acids are post-translationally removed from the C-terminal end of the beta-lactamase enzyme from B. imaginarium (i.e. - after it is translated and released from the ribosome, a protease chews off a few amino acids). The wild-type enzyme, which has had the amino acids removed from the C’-terminus, is 327 amino acids in length and the C-terminal amino acids are shown below aligned with the C-terminal amino acids of a frameshift mutant, which is not processed at its C-terminus. The wildtype and frameshift mutant have identical coding sequences except for the insertion or deletion of a single nucleotide in the sequences encoding the C-terminal region of the protein. Use this information to answer the questions below.

AA#: 327

wild-type: Asn Met Asn Gly Lys

mutant: Asn Met Ile Trp Gln Met Cys Asp Met Lys Asp

A. What was the mutational event that gave rise to the frameshift mutant? (identify which codon contains the inserted or deleted nucleotide and the position within the codon where the mutation occurred.

B. Deduce the number of amino acids in the wild-type enzyme prior to processing of the C-terminus and, as far as possible, the actual sequence of the C-terminus of the wild-type enzyme

Explanation / Answer

wild-type: Asn Met Asn Gly Lys

aac atg aac GGN AAR

Mutant Sequence - aac atg att tgg cag atg tgc gat atg aaa gat

mutant protein - Asn Met Ile trp Gln Met Cys Asp Met Lys Asp

Asn is coded by codon AAC and AAU.

AUU, AUC and AUA are the codons for Ile.

So for Asn to Ile mutation, the change can be

AAC------------> AUC

AAU------------>AUU

The mutation is not due to a single insertion or deletion. It is an 'indel' resulting in the mutant transcript

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