Nucleotide metabolism in Lactic Acid Bacteria

Nucleotides are not only precursors in the synthesis of RNA og DNA, but are constituting vital parts of coenzymes in the biosynthesis of proteins, phospholipides og polysaccharides. Furthermore, nucleotides acts as allosteric effectors in a large number of enzymatic reactions, and due to their role as energy transporters, they are directly involved in the different metabolic pathways, including stress response and glycolysis. In most organisms nucleotides are made either de novo or from prefabricated nucleosides og nucleobases, already present in the growth medium or formed intracellulary from nucleic acid turnover, through the socalled salvage pathways.
A number of genes involved in nucleotide metabolism have been cloned, sequenced and characterised. Furthermore the majority of reactions in pyrimidine metabolism has been characterised, including the development of powerful procedures for positive selection of mutants in most of the pyrimidine salvage genes. Results obtained during the analysis of both purine og pyrimidine biosyntetic genes, have shown, that the expression of these genes are regulated in at least two fundamentally different ways. A knowledge of the mechanism by which these genes are regulated, will be of the utmost importance for the understanding of interactions among metabolic pathways in the individual cell.