Functional analysis of three amino acid residues of purR repressor, Trp147, Gln-218 and Gln-292 in Salmonella typhimurium

The amber mutation sites of 6 purR(am) mutants were determined by cloning and DMA sequencing. The results showed that the mutations were distributed at three different sites in PurR coding region, G721(→A), C933(→T) and C1155(→T), which respectively turn Trp-147,Gln-218 and Gln-292 of PurR into TAG terminal codon. To determine the effect of the three amino acid residues on regulatory function of PurR protein 5 different kinds of tRNA suppressor genes, Su3, Su4, Su6, Su7 and Su9 were used for creating the PurR protein variants with single amino acid substitution. The results indicated that Cys, Glu, Gly, His and Arg which substituted Trp-147 respectively all could not recover the regulation function of PurR. It confirmed that Trp-147 is a critical amino acid for the PurR function. Gln-292 substituted respectively by the same amino acids also could not recover the PurR function, demonstrating that Gln-292 is also an important amino acid residue in PurR.

Functional analysis of three amino acid residues of purR repressor, Trp147, Gln-218 and Gln-292 in Salmonella typhimurium