The bacterial cell coordinates the 2OOO individual chemical reactions necessary for its growth and survival by controls that operate above the level of the individual operon. Many operons, though scattered on the genetic map, are organized as systems of genes (regulons) sharing a common regulatory molecule. This project explores the regulons involved in the global response of Escherichia coli to high temperature, to low temperature, and to phosphate starvation. (i) A shift to high temperature (42 degree C) induces a set of 18 heat-shock genes. This response system is one of the most ancient regulons, and its near universal retention throughout biology speaks to some essential but still unknown role common to cells from bacterial to human. Heat-shock function will be studied by identifying the products of individual heat-shock genes and learning their functions, and by studying mutant cells defective in the heat-shock response or genetically engineered cells to produce a heat-shock response upon artificial induction. (ii) A shift to low temperature (10 degree C) induces a different set of proteins, including polynucleotide phosphorylase, NusA, translation initiation factors 2 alpha and 2 beta, and a very prominently induced 10kd protein of unknown identity. Analysis of this cold shock response is designed to learn how E. coli adapts to low temperature, to discover whether the cold-shock induced proteins form a regulon, and to answer some long standing questions about the function and regulation of these proteins, particularly concerning the coupling of transcription and translation during growth. (iii) Starvation for phosphate induced approximately 100 proteins in E. coli, some of which are governed by multiple genes whose products serve as sensors and regulators. By measuring the total cellular protein response to phosphate limitation in mutants defective in one or more element of this complex regulatory system, the regulon organization of the response will be analyzed, and its multiple functions studied. This study should help in understanding how regulons coordinate gene expression for growth and for survival of E. coli in the face of environmental stress, and should provide valuable leads to metabolic integration and gene coordination in more complete cells. ln addition, the heat-shock response has human medical implications for bacterial and virus infections, for environmentally induced birth defects, for tumor chemotherapy, and for cell responses to environmental stress.
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