title: Physiological characterization of Escherichia coli rpoB mutants with abnormal control of ribosome synthesis.
abstract: We have previously reported the isolation of Escherichia coli rpoB mutants in which the control of ribosome synthesis by the nucleotide effector guanosine tetraphosphate (ppGpp) is altered, owing to a 20-fold increased sensitivity of the mutant RNA polymerases to ppGpp. In these mutants, the level of ppGpp during exponential growth is decreased about 10-fold, relative to that of rpoB+ wild-type strains, such that a near normal partitioning of RNA polymerase occurs with respect to stable RNA (rRNA and tRNA) gene activity. Here, the physiological effects of two different rpoB alleles in a relA+ and relA background were analyzed in greater detail by comparison with their isogenic rpoB+ wild-type parents. For a given growth medium, the rpoB mutations were found to affect four parameters which resulted in a reduction of growth rate. The results reinforce a previous conclusion that a key element in control of the bacterial growth rate is a mutual relationship between control of ribosome synthesis by ppGpp and control of relA-independent ppGpp metabolism by the concentration and function of ribosomes.
mesh_terms: D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D005798:Genes, Bacterial; D006150:Guanine Nucleotides / Q000378:metabolism*; D006159:Guanosine Tetraphosphate / Q000378:metabolism*; D009154:Mutation; D012329:RNA, Bacterial / Q000096:biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis; D012335:RNA, Ribosomal / Q000096:biosynthesis; D012343:RNA, Transfer / Q000096:biosynthesis; D012270:Ribosomes / Q000378:metabolism*
chemical_list: D006150:Guanine Nucleotides; D012329:RNA, Bacterial; D012333:RNA, Messenger; D012335:RNA, Ribosomal; D006159:Guanosine Tetraphosphate; D012343:RNA, Transfer; D012321:DNA-Directed RNA Polymerases