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pdxK encodes a pyridoxine (PN)/pyridoxal (PL)/pyridoxamine (PM) kinase thought to function in the salvage pathway of pyridoxal 5′-phosphate (PLP) coenzyme biosynthesis. The observation thatpdxK null mutants still contain PL kinase activity led to the hypothesis thatEscherichia coli K-12 contains at least one other B6 -vitamer kinase. Here we support this hypothesis by identifying thepdxY gene (formally, open reading framef287b ) at 36.92 min, which encodes a novel PL kinase. PdxY was first identified by its homology to PdxK in searches of the completeE. coli genome. Minimal clones ofpdxY + overexpressed PL kinase specific activity about 10-fold. We inserted an omega cassette intopdxY and crossed the resultingpdxY ::ΩKanr mutation into the bacterial chromosome of apdxB mutant, in which de novo PLP biosynthesis is blocked. We then determined the growth characteristics and PL and PN kinase specific activities in extracts ofpdxK andpdxY single and double mutants. Significantly, the requirement of thepdxB pdxK pdxY triple mutant for PLP was not satisfied by PL and PN, and the triple mutant had negligible PL and PN kinase specific activities. Our combined results suggest that the PL kinase PdxY and the PN/PL/PM kinase PdxK are the only physiologically important B6 vitamer kinases inE. coli and that their function is confined to the PLP salvage pathway. Last, we show thatpdxY is located downstream frompdxH (encoding PNP/PMP oxidase) and essentialtyrS (encoding aminoacyl-tRNATyr synthetase) in a multifunctional operon.pdxY is completely cotranscribed withtyrS , but about 92% oftyrS transcripts terminate at a putative Rho-factor-dependent attenuator located in thetyrS-pdxY intercistronic region.

journal of bacteriology

Identification and Function of the <i>pdxY</i> Gene, Which Encodes a Novel Pyridoxal Kinase Involved in the Salvage Pathway of Pyridoxal 5′-Phosphate Biosynthesis in <i>Escherichia coli</i> K-12

Identification and Function of the pdxY Gene, Which Encodes a Novel Pyridoxal Kinase Involved in the Salvage Pathway of Pyridoxal 5′-Phosphate Biosynthesis in Escherichia coli K-12