Chemical mutagenesis and DNA synthesis in cdc8, a DNA replication mutant of Saccharomyces cerevisiae

Cloning, expression in Escherichia coli, and characterization of Arabidopsis thaliana UMP/CMP kinase

A cDNA encoding the Arabidopsis thaliana uridine 5'-monophosphate (UMP)/cytidine 5'-monophosphate (CMP) kinase was isolated by complementation of a Saccharomyces cerevisiae ura6 mutant. The deduced amino acid sequence of the plant UMP/CMP kinase has 50% identity with other eukaryotic UMP/CMP kinase proteins. The cDNA was subcloned into pGEX-4T-3 and expressed as a glutathione S-transferase fusion protein in Escherichia coli. Following proteolytic digestion, the plant UMP/CMP kinase was purified and analyzed for its structural and kinetic properties. The mass, N-terminal sequence, and total amino acid composition agreed with the sequence and composition predicted from the cDNA sequence. Kinetic analysis revealed that the UMP/CMP kinase preferentially uses ATP (Michaelis constant [Km] = 29 microM when UMP is the other substrate and Km = 292 microM when CMP is the other substrate) as a phosphate donor. However, both UMP (Km = 153 microM) and CMP (Km = 266 microM) were equally acceptable as the phosphate acceptor. The optimal pH for the enzyme is 6.5. P1, P5-di(adenosine-5') pentaphosphate was found to be a competitive inhibitor of both ATP and UMP.

International Commission for Protection Against Environmental Mutagens and Carcinogens. Deoxyribonucleoside triphosphate levels: a critical factor in the maintenance of genetic stability

DNA precursor pool imbalances can elicit a variety of genetic effects and modulate the genotoxicity of certain DNA-damaging agents. These and other observations indicate that the control of DNA precursor concentrations is essential for the maintenance of genetic stability, and suggest that factors which offset this control may contribute to environmental mutagenesis and carcinogenesis. In this article, we review the biochemical and genetic mechanisms responsible for regulating the production and relative amounts of intracellular DNA precursors, describe the many outcomes of perturbations in DNA precursor levels, and discuss implications of such imbalances for sensitivity to DNA-damaging agents, population monitoring, and human diseases.