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 phosphorylated by thiamin-monophosphate kinase (EC 2.7.4.16) to form thiamin pyrophosphate. We have isolated and 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 activity. thiL was located in the 10-centisome region of the S. typhimurium chromosome. We demonstrated that altered thiamin-monophosphate kinase activity resulted in decreased repression of transcription of thiamin pyrophosphate-regulated thiamin biosynthetic genes. In contrast to other thi loci, thiL is not transcriptionally regulated by thiamin pyrophosphate. This result is consistent with a dual role for ThiL in de novo biosynthesis and in salvage of exogenous thiamin.