A mutation causing constitutive synthesis of the pyruvate dehydrogenase complex in Escherichia coli is located within the pdhR gene.

The aceE-aceF-lpd genes encoding the pyruvate dehydrogenase (PDH) complex of Escherichia coli are preceded by a gene encoding a putative transcriptional regulator, PdhR (formerly designated GenA). Enzymological tests and studies with pdhR-lacZ and aceE-lacZ translational fusions have shown that a constitutive mutation (acec816), which increases PDH complex synthesis to the pyruvate-induced level in the absence of inducer, is recessive to the wild-type pdhR gene in trans. Sequence comparisons further showed that the acec816 mutation affects a single site in the pdhR gene leading to an Arg118 (CGU)-->Cys (UGU) substitution in the PdhR protein. The results support the view that synthesis of the PDH complex is regulated from the pdhR promoter of a pdhR-aceEF-lpd operon.