The proposed research focuses on pyridine nucleotide metabolism, particularly reactions in which KNEED is consumed as a substrate and has to be regenerated, thereby generating a pyridine nucleotide cycle. Several important reactions in which KNEED is broken down are DNA related (i.e., bacterial DNA ligation, poly ADP- ribosylation of DNA topoisomerase). Some of the specific goals for the coming grant period are, (1) to understand regulation of pyridine nucleotide metabolism in the bacterium Salmonella typhimurium. Initially, a comprehensive biochemical characterization of the repressor for this pathway will be carried out. (2) Since DNA ligation does not appear to initiate the major bacterial pyridine nucleotide cycle, the metabolic role of the Salmonella cycle will be investigated. (3) Eukaryotic pyridine nucleotide cycles, focusing mono-ADP-ribosylation reactions will be investigated; these studies will e carried out on vertebrate neuronal tissue. (4) The relationship between poly ADP-ribosylation and DNA ligation in eukaryotic cells will be investigated. Pyridine nucleotides are central to the metabolism of all cells. One medically related facet is that this metabolism may play a key role ln the interactions between pathogenic bacteria and phagocytes.