Initiation of chromosomal DNA replication is a key control point in the prokaryotic cell cycle and in the determination of eukaryotic cellular quiescence or proliferation. We are investigating the participation of the cell membrane in the regulation of DN A replication in E. coli. Mutagenesis and protein chemistry techniques are being employed to study the interaction between acidic phospholipids and the initiator protein, DnaA, and how their association participates in the cell-cycle control of chromosoma l replication. A second project in the laboratory focuses on understanding the physiological role that cellular inorganic polyphosphates play in how cells respond to environmental stresses. These long, energy-rich polymers are found found in virtually all organisms. Disruption of the gene that encodes the polyphosphate biosynthetic enzyme, polyphosphate kinase (PPK), gives rise to cells that have decreased viability following exposure to environmental challenges such as heat, UV-irradiation and oxidative stress, or when the cells are maintained in the stationary phase for prolonged periods. Certain mutations elsewhere in the genome have the ability to suppress the sensitivities that ppk knock-out cells have toward these environmental stresses. Our identification of the genes that harbor such mutations will help us understand in which signal transduction and stress response pathways polyphosphates participate.