GENETIC AND PHYSIOLOGICAL CHARACTERIZATION OF A FORMATE-DEPENDENT 5'-PHOSPHORIBOSYL-1-GLYCINAMIDE TRANSFORMYLASE ACTIVITY IN BACILLUS-SUBTILIS

We have found that Bacillus subtilis possesses a second 5'-phosphoribo syl-1-glycinamide (GAR) transformylase catalysing the first one-carbon transfer reaction in the purine biosynthetic pathway. Inactivation of the purN gene encoding the N-10-formyl tetrahydrofolate-dependent enz yme did not result in purine auxotrophy. However, growth of a purN str ain was stimulated when either purine or formate was added to the grow th medium. In cell-free extracts GAR could be formylated, provided for mate was added to the assay mixture. From the purN strain, purine-requ iring mutants were isolated. One of these mutant strains was defective in the formate-dependent formylation of GAR in vitro. The gene contai ning this second mutation was designated purT, and was mapped to appro ximately 20 degrees on the genetic map between the cysA and aroI marke rs.