9318479 Slocum Pyrimidine nucleotides are precursors of DNA and RNA synthesis and pyrimidine derivatives are activated intermediates in many other types of biosyntheses. These processes are of fundamental importance to the growth and development of all living organisms. In plants, little is known about the various mechanisms which regulate pyrimidine biosynthesis, but most evidence suggests that the important sites of regulation are the first and/or second steps of the pathway, involving the enzymes carbamoylphosphate synthetase (CPSase) and aspartate transcarbamoylase (ATCase). The objective of this research is to investigate the various molecular mechanisms regulating the activity of these enzymes in plants. This will be accomplished by cloning the genes for CPSase and ATCase, purifying and biochemically characterizing the enzyme proteins, and producing CPSase and ATCase-specific antisera. The nucleic acid and antibody probes will be used to investigate expression of the genes encoding CPSase and ATCase in different plant tissues and in response to various treatments that would be expected to impact pyrimidine biosynthesis. The genes encoding CPSase and ATCase will be cloned by functional complementation in E. coli carA/B- and pyrB- mutants. This approach has already permitted the successful isolation of two different genes (pyrB1 and pyrB2) encoding functional ATCases in pea. This plant is the first organism in which more than one pyrB gene has been demonstrated. ***
