THE APBE GENE ENCODES A LIPOPROTEIN INVOLVED IN THIAMINE SYNTHESIS INSALMONELLA-TYPHIMURIUM

Thiamine pyrophosphate is an essential cofactor that is synthesized de novo in Salmonella typhimurium. The biochemical steps and gene produc ts involved in the conversion of aminoimidazole ribotide (AIR), a puri ne intermediate, to the 4-amino-5-hydroxymethyl-2-methyl pyrimidine (H MP) moiety of thiamine have yet to be elucidated, We have isolated mut ations in a new locus (Escherichia coil open reading frame designation yojK) at 49 min on the S. typhimurium chromosome, Two significant phe notypes associated with lesions in this locus (apbE) were identified, First, apbE purF double mutants require thiamine, specifically the HMP moiety, Second, in the presence of adenine, apbE single mutants requi re thiamine, specifically both the HMP and the thiazole moieties, Toge ther, the phenotypes associated with apbE mutants suggest that flux th rough the purine pathway has a role in regulating synthesis of the thi azole moiety of thiamine and are consistent with ApbE being involved i n the conversion of AIR to HMP. The product of the apbE gene was found to be a 36-kDa membrane-associated lipoprotein, making it the second membrane protein implicated in thiamine synthesis.