guanosine-tetraphosphate and Chromosome-Deletion

It was known previously that 1) the relA gene of Escherichia coli encodes an enzyme capable of guanosine 3',5'-bispyrophosphate (ppGpp) synthesis, 2) an uncharacterized source of ppGpp synthesis exists in relA null strains, and 3) cellular degradation of ppGpp is mainly due to a manganese-dependent ppGpp 3'-pyrophosphohydrolase encoded by the spoT gene. Here, the effects of spoT gene insertions and deletions are compared with analogous alterations in neighboring genes in the spo operon and found to be lethal in relA+ strains as well as slower growing in relAl backgrounds than delta relA hosts. Cells with null alleles in both the relA and spoT genes are found no longer to accumulate ppGpp after glucose exhaustion or after chelation of manganese ions by picolinic acid addition; the inability to form ppGpp is reversed by a minimal spoT gene on a multicopy plasmid. Strains apparently lacking ppGpp show a complex phenotype including auxotrophy for several amino acids and morphological alterations. We propose that the SpoT protein can either catalyze or control the alternative pathway of ppGpp synthesis in addition to its known role as a (p)ppGpp 3'-pyrophosphohydrolase. We favor the possibility that the SpoT protein is a bifunctional enzyme capable of catalyzing either ppGpp synthesis or degradation.

Topics: Alleles; Amino Acids; Blotting, Southern; Chromosome Deletion; DNA, Bacterial; Escherichia coli; Genes, Bacterial; Guanosine Tetraphosphate; Mutation; Operon; Plasmids

Using the set of transducing lambda phages the gpp gene, responsible for pppGpp to ppGpp conversion, was localized between rep and trxA genes on 85 min of the Escherichia coli genetic map. Taking advantage of the Tn10 transposon inserted into the adjacent ilvY locus, we deleted the region of E. coli chromosome covering ilvC, rep and gpp genes. The metabolism of (p)ppGpp in the deletion-containing cells confirms that the product of the gpp gene, guanosine pentaphosphatase, is not the only enzyme, responsible for pppGpp degradation and ppGpp synthesis.

Topics: Bacteriophage lambda; Chromosome Deletion; Chromosome Mapping; Chromosomes, Bacterial; Escherichia coli; Genes, Bacterial; Guanine Nucleotides; Guanosine Tetraphosphate; Transduction, Genetic

We have located the DNA sequence involved in the stringent control of the Escherichia coli tufB operon. Various deletion and insertion mutants of the promoter locus were constructed by in vitro mutagenesis, and their response to guanosine-5'-diphosphate-3'-diphosphate (ppGpp) was examined in a cell-free transcription system consisting of purified RNA polymerase holoenzyme. The nucleotide sequence (GpCpGpC) from positions -7 to -4 (designating the initiation site of mRNA as position +1) is responsible for the selective inhibition by ppGpp of tufB transcription. Point mutations were then constructed in which each one of the above four nucleotides was replaced by an A or T residue and tested for their response to ppGpp in the in vitro transcription system. The results indicated that the alteration of any nucleotide in the GpCpGpC sequence leads to the loss of the stringent response.

Topics: Base Sequence; Chromosome Deletion; DNA Restriction Enzymes; Escherichia coli; Genes; Genes, Bacterial; GTP Pyrophosphokinase; Guanosine Tetraphosphate; Mutation; Operon; Phosphotransferases; Transcription, Genetic