Question

1. Some 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 some amino acids).  The wild-type enzyme, which has had the amino acids removed from the C’-terminus, is 246 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 – due to a frameshift mutation - 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 DNA encoding the C-terminal region of the protein.  Use this information to answer the questions below.                   

codon#: 243 244 245 246

wt: gly leu   asn ser-COOH

mutant:   gly his gln gln thr  trp met asn his glu  gly-COOH

1. 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.
2. Deduce the number of amino acids in the wild-type enzyme prior to processing of the C-terminus.
3. Deduce,as far as possible, the sequence of the C-terminus of the wild-type enzyme prior to processing (you will not get a unique answer due to the degeneracy of the genetic code).

Answer 1

The mutational event was an addition of an extra nucleotide in the last codon (244).

The number of amino acids in the wild-type enzyme prior to being processed is 246/3 = 82.

The sequence of the C-terminus of the wild-type enzyme prior to processing is GGUUUAAAUAGU.