ANALYSIS OF ABRB MUTATIONS, MUTANT PROTEINS, AND WHY ABRB DOES NOT UTILIZE A PERFECT CONSENSUS IN THE -35-REGION OF ITS SIGMA(A) PROMOTER

The Bacillus subtilis global regulator AbrB is a DNA-binding protein c omposed of six identical monomers of 96 amino acids that shows specifi city to the promoter regions of its target genes including its own, We have sequenced thirteen previously uncharacterized abrB mutations, Fo ur mutant AbrB proteins were purified, and their DNA-binding propertie s and multimeric structures were examined, AbrB23 (R25S) had no apprec iable DNA binding activity but retained a hexameric structure, indicat ing that Arg25 is important in DNA interactions, Three other mutant pr oteins, AbrB1 (C56Y), AbrB19 (Gln(83) --> termination codon), and AbrB 100 (L69P), showed decreased DNA binding and altered multimeric intera ctions, Analysis of the expression and AbrB binding affinities of muta nt abrB promoters demonstrated that a consensus -35 region is incompat ible with proper autoregulation of the abrB gene.