IDENTIFICATION AND CHARACTERIZATION OF AN OPERON IN SALMONELLA-TYPHIMURIUM INVOLVED IN THIAMINE BIOSYNTHESIS

Thiamine pyrophosphate (TPP) is synthesized de novo in Salmonella typh imurium and is a required cofactor for many enzymes in the cell. Five kinase activities have been implicated in TPP synthesis, which involve s joining a 4-methyl-5-(beta-hydroxyethyl) thiazole (THZ) moiety and a 4-amino-5-hydroxymethyl-2-methylpyrimidine (HMP) moiety. We report he re identification of a 2-gene operon involved in thiamine biosynthesis and present evidence that the genes in this operon, thiMD, encode two previously identified kinases, THZ kinase and HMP phosphate (HMP-P) k inase, respectively. We further show that this operon belongs to the g rowing class of genes involved in TPP synthesis that are transcription ally regulated by TPP, Our data are consistent with ThiM being a salva ge enzyme and ThiD being a biosynthetic enzyme involved in TPP synthes is, as previously suggested.