THE THIJ LOCUS AND ITS RELATION TO PHOSPHORYLATION OF HYDROXYMETHYLPYRIMIDINE IN ESCHERICHIA-COLI

Extracts from Escherichia coli K-12 contained two distinct enzymes cap able of catalysing the phosphorylation of hydroxymethylpyrimidine (HMP ) to HMP monophosphate: pyridoxine kinase (EC 2.7.1.35) and an enzyme that has not previously been genetically analysed, HMP kinase (EC 2.7. 1.49). Two distinct genes, pdxL and thiJ, specify the activities of th e former and latter enzymes, respectively; The inactivation of both ge nes by independent mutations in the same cell resulted in the complete loss of HMP kinase activity. Experiments with a series of strains tha t carry mutations in thiC, thiC pdxB, thiC pdxB pdxL and thiC pdxB pdx L thiJ revealed that the ability of the double mutant (pdxL thiJ) to u tilize HMP in thiamin pyrophosphate biosynthesis was restored by intro ducing the wild-type allele corresponding to the thiJ mutation. The th iJ locus was mapped on the chromosome near the thiD and thiM loci, whi ch govern the activities of phosphomethylpyrimidine kinase (EC 2.7.4.7 ) and hydroxyethylthiazole kinase (EC 2.7.1.50), respectively.