View article

The threonine dehydratase IlvA is part of the isoleucine biosynthesis pathway in the Gram‐positive model bacterium Bacillus subtilis. Consequently, deletion of ilvA causes isoleucine auxotrophy. It has been reported that ilvA pseudo‐revertants having a derepressed hom‐thrCB operon appear in the presence of threonine. Here we have characterized two classes of ilvA pseudo‐revertants. In the first class the hom‐thrCB operon was derepressed unmasking the threonine dehydratase activity of the threonine synthase ThrC. In the second class of mutants, threonine biosynthesis was more broadly affected. The first class of ilvA pseudo‐revertants had a mutation in the P_hom promoter (P*_hom), resulting in constitutive expression of the hom‐thrCB operon. In the second class of ilvA pseudo‐revertants, the thrR gene encoding a putative DNA‐binding protein was inactivated, also resulting in constitutive expression of the …