T41 mutation in lac repressor is Tyr282----Asp.

A monomeric mutant of the lac repressor protein, designated T41, produced originally by the in vivo MutT mutagenesis exhibited behavior similar to mutants identified as Tyr282----Ser or Tyr282----Gln [Schmitz et al., J. Biol. Chem. 251 (1976) 3359-3366]. The T41 gene, encoded within a phage lambda prophage in the Escherichia coli genome, was amplified by polymerase chain reaction and sequenced. The only mutation found in the nucleotide sequence corresponded to position 282 in the protein, and the amino acid encoded was Asp. The Tyr282----Asp mutant protein produced by site-specific methods was isolated and shares the oligomeric and inducer binding characteristics previously determined for the T41 mutation.