Isolation and characterization of a purC(orf)QLF operon from Lactococcus [correction of Lactobacillus] lactis MG1614.

We have isolated genes encoding enzymes of the de novo purine nucleotide biosynthesis pathway from Lactococcus lactis MG1614 by colony hybridization using DIG-labeled DNA probes. The organization of the genes needed for the de novo biosynthesis of purine nucleotides in L. lactis differs from that found in other organisms. In L. lactis there is a gene cluster, which contains five out of the 11 genes needed for the de novo biosynthesis of IMP, namely purC, orf, purQ, purL and purF. These genes were shown to be transcribed as a single transcription unit by Northern hybridization analysis. The 5' end of the transcript of the purC(orf)QLF operon was determined by primer extension analysis using fluorescently end-labeled probes. The purC(orf)QLF operon of L. lactis is transcribed in Escherichia coli, and the gene product of the purF gene, glutamine phosphoribosylpyrophosphate amidotransferase (glutamine PRPP ATase, EC 2.4.2.14), can functionally complement the E. coli purF mutant strain TX158. We also show that the promoter of the purC(orf)QLF operon is regulated in response to exogenously added purines.