Organization and regulation of genes for de novo purine nucleotide synthesis in Bacillus subtilis

Regulation of purine nucleotide biosynthesis: in yeast and beyond

Purine nucleotides are critically important for the normal functioning of cells due to their myriad of activities. It is important for cells to maintain a balance in the pool sizes of the adenine-containing and guanine-containing nucleotides, which occurs by a combination of de novo synthesis and salvage pathways that interconvert the purine nucleotides. This review describes the mechanism for regulation of the biosynthetic genes in the yeast Saccharomyces cerevisiae and compares this mechanism with that described in several microbial species.

Cloning and expression of the Lactococcus lactis purDEK genes, required for growth in milk

An operon containing the genes purD and purE and part of the purK gene was cloned from the facultative anaerobic gram-positive bacterium Lactococcus lactis by complementation of the purD mutation in Escherichia coli SO609. The genes encode enzymes in the de novo pathway of purine nucleotides. The expression of the genes was regulated approximately 35-fold at the transcription level by the availability of purines in the growth medium. Deletion analysis of the nucleotide region upstream of purD indicated that a region of 145 bp is enough to give regulated expression of the reporter lacLM genes, which encode beta-galactosidase. Deletion of a region 79 bp upstream of the transcription start point reduced the promoter activity 33-fold when incubated in a purine-free medium and to values below the detection limit when incubated in a purine-containing medium. No secondary transcription start points were mapped in or close to this region, indicating that a putative activator site and not a promoter was deleted or partly destroyed.

Identification of a purC gene from Streptococcus pneumoniae

A gene encoding 5'-phosphoribosyl-5-aminoimidazole-4-N-succinocarboxamide synthetase was identified in Streptococcus pneumoniae as a 708-bp segment of the genome encoding a 27,001-Da protein with strong similarity to known PurC proteins. The S. pneumoniae purC gene, found immediately adjacent to the competence induction genes, comAB, was cloned and sequenced. The predicted protein product of purC displayed substantial (> 40%) identity to the entire sequence of the PurC proteins of Bacillus subtilis and Escherichia coli. Function of the S. pneumoniae gene product was demonstrated by complementation of E. coli purC mutations.