MUTATIONAL STUDY AT SER300 POSITION OF THE ESCHERICHIA-COLI LACTOSE REPRESSOR

We have previously reported that a Ser300Asn mutant of the Escherichia coli lactose repressor protein produced a temperature-sensitive pheno type. In order to analyze the structure-function relationship of the l actose repressor protein, we conducted 18 amino acid substitutions at this Ser300 site by using in vitro mutagenesis. The substitutions at t his position that exhibited repressors with the wild-type phenotype in vivo were Gly, Ala, Ile, Thr, Met and Cys; the other 10 substitutions examined (Leu, Val, Tyr, Trp, Asp, Gin, Gin, His, Lys and Arg) result ed in the lacI(-) phenotype. In addition, the Ser300Phe mutation resul ted in the lacI(ts) phenotype, while the Ser300Pro mutation resulted i n lacI(ts,s). It seems likely that the Ser300 position plays an import ant role in oligomer formation and inducer binding. (C) Academic Press , Inc.