Common element in the repression control of enzymes of histidine and aromatic amino acid biosynthesis in Bacillus subtilus.

Single-step mutants of Bacillus subtilis derepressed for enzymes of both aromatic amino acid and histidine biosynthesis were isolated. These mutants occur at a frequency of 10(-6) per cell per generation. All histidine enzymes as well as all enzymes of aromatic acid synthesis which were examined are maximally derepressed. This level cannot be repressed by growth on either histidine or tyrosine. Some of the structural genes which specify the derepressed enzymes are linked to the aromatic cluster; others are unlinked. The significance of these nonrepressible strains is discussed in terms of the mechanism of repression.