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

Abstract
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 Gen A). 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.

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