CHARACTERIZATION OF THIL, ENCODING THIAMIN-MONOPHOSPHATE KINASE, IN SALMONELLA-TYPHIMURIUM

Thiamin pyrophosphate is an essential cofactor that is synthesized de novo by Salmonella typhimurium. In bacteria, the end product of the de novo biosynthetic pathway is thiamin monophosphate, which is then pho sphorylated by thiamin-monophosphate kinase (EC 2.7.4.16) to form thia min pyrophosphate, We have isolated anti characterized the thiL, gene of S. typhimurium and showed that thiL is a 978-base pair open reading frame encoding a 35-kDa protein with thiamin-monophosphate kinase act ivity. thiL, was located in the 10-centisome region of the S. typhimur ium chromosome, We demonstrated that altered thiamin-monophosphate kin ase activity resulted in decreased repression of transcription of thia min pyrophosphate-regulated thiamin biosynthetic genes. In contrast to other thi loci, thiL is not transcriptionally regulated bg thiamin py rophosphate. This result is consistent with a dual role for ThiL in de novo biosynthesis and in salvage of exogenous thiamin.