Question

An important validation of the genetic code occurred when George Streisinger determined the amino acid sequence of bacteriophage T4 lysozyme and of mutants induced by proflavin, a dye with a planar structure that can intercalate (fit) between successive base pairs in DNA and induce frameshift mutations−that is, mutations involving additions or deletions of a single base. Streisinger and colleagues found that a particular single-base insertion mutation could be suppressed, with wild-type function restored, by a mutation that evidently involved a single-base deletion at a nearby site. In another such analysis, the Streisinger group found that the altered amino acid sequence in the affected part of the double mutation involved addition of one amino acid, as shown below.

Wild-type ...Lys-Ser-Pro-Ser-Leu-Asn-Ala...

Double mutant ...Lys-Ser-Val-His-His-Leu-Met-Ala...

Part A

Explain how this result is compatible with the codon assignments determined in vitro.

Match the words in the left column to the appropriate blanks in the sentences on the right.

Reset Help one-base deletion assumption ls that the first mutation Invand that the second mutation lengthening restored the reading frame with a with the one-amino acid of the polypeptide chain representing acceptable missense. shortening two-base deletion one-base insertion two-base insertion SubmitRequest An

Answer 1

The assumption is that the first mutation involved a "one base insertion" and that the second mutation restored the reading frame with a "one base deletion" , with the one amino acid "lengthening" of the polypeptide chain representing acceptable missense.