MUTATIONS IN BACILLUS-SUBTILIS PYRR, THE PYR REGULATORY PROTEIN, WITHDEFECTS IN REGULATION BY PYRIMIDINES

The pyrimidine nucleotide biosynthetic (pyr) operon in Bacillus subtil is is regulated by a transcriptional attenuation mechanism in which Py rR, a bifunctional pyr RNA-binding attenuation protein/uracil phosphor ibosyltransferase, plays a crucial role. A convenient procedure for is olation of pyrR mutants with defects in the regulation of pyr operon e xpression is described, The selection is based on the selection of spo ntaneous mutations that convert the pyrimidine-sensitive growth of cpn strain (lacking arginine-repressible carbamyl phosphate synthetase) t o pyrimidine resistance. Twelve such mutants were isolated and sequenc ed. All resulted from point mutations in the pyrR gene.