CHARACTERIZATION OF THII A NEW GENE INVOLVED IN THIAZOLE BIOSYNTHESISIN SALMONELLA-TYPHIMURIUM

Thiamine pyrophosphate (TPP) is a required cofactor in Salmonella typh imurium that is generated de novo by the condensation of 4-amino-5-hyd roxymethyl pyrimidine (HMP) pyrophosphate and 4-methyl-5-(beta-hydroxy ethyl)-thiazole (THZ) monophosphate. The THZ and HMP moieties are inde pendently synthesized, and labeling studies have demonstrated probable metabolic precursors to both. We present herein the initial character ization of thiI, a gene required for THZ synthesis. We show that thiI is a 1,449-bp open reading frame located at minute 9.65 on the S. typh imurium chromosome and that it encodes a 483-amino-acid protein with a predicted molecular mass of 55 kDa. Unlike genes in the thiamine bios ynthetic operon at minute 90, thiI is not transcriptionally regulated by TPP.