1) Crick and Brenner were able to combine two T4 rllB mutants (one mutant genera

Question

1) Crick and Brenner were able to combine two T4 rllB mutants (one mutant generated by addition (+) of a nucleotide and the second mutant generated by deletion (-) of a mutant) by recombination to recover the wild-type T4 phage. The RNA-like strand of the wild-type and the recombined portion of the double mutant is shown below as codons Wild-type 5' AAA AGT CCA TCACTT AAT GCC 3' Mutant 5' AAA GTC CAT CAC TTA ATG GCC3" a. Which nucleotide is added and deleted in the mutant DNA? b. The recombined double mutant produces wild-type phenotype. What alterations in amino acids occurred in this double mutant? c) How can you explain the fact that amino acids are different in the double mutant than in the wild type protein, yet the T4 phage has a wild-type phenotype.

Explanation / Answer

a-Adenine nucleotide is removed and Guanine nucleotide is added.

b-In mutant DNA the amino acid sequence is changed between Lysin and alanine.

c-mutant DNA is different from wild type by amino acid sequence. The amino acid sequence of wild type is -

Lysine serine Proline serine leucine Asparagine alanine.

Amino acid sequence of mutant DNA -

Lysine valine histidine histidine leucine methionine alanine.

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