Glutamyl-gamma-methyl ester acts as a methionine analogue in Escherichia coli: analogue resistant mutants map at the metJ and metK loci

Linkage map of Escherichia coli K-12, edition 10: the traditional map

This map is an update of the edition 9 map by Berlyn et al. (M. K. B. Berlyn, K. B. Low, and K. E. Rudd, p. 1715-1902, in F. C. Neidhardt et al., ed., Escherichia coli and Salmonella: cellular and molecular biology, 2nd ed., vol. 2, 1996). It uses coordinates established by the completed sequence, expressed as 100 minutes for the entire circular map, and adds new genes discovered and established since 1996 and eliminates those shown to correspond to other known genes. The latter are included as synonyms. An alphabetical list of genes showing map location, synonyms, the protein or RNA product of the gene, phenotypes of mutants, and reference citations is provided. In addition to genes known to correspond to gene sequences, other genes, often older, that are described by phenotype and older mapping techniques and that have not been correlated with sequences are included.

Lack of S-adenosylmethionine results in a cell division defect in Escherichia coli

The enzyme S-adenosylmethionine (SAM) synthetase, the Escherichia coli metK gene product, produces SAM, the cell's major methyl donor. We show here that SAM synthetase activity is induced by leucine and repressed by Lrp, the leucine-responsive regulatory protein. When SAM synthetase activity falls below a certain critical threshold, the cells produce long filaments with regularly distributed nucleoids. Expression of a plasmid-carried metK gene prevents filamentation and restores normal growth to the metK mutant. This indicates that lack of SAM results in a division defect.

The leucine regulon of Escherichia coli K-12: a mutation in rblA alters expression of L-leucine-dependent metabolic operons

We have isolated and characterized a highly pleiotropic Escherichia coli mutant affected in the activity of a number of enzymes involved in different metabolic pathways, all of which are regulated by leucine. Selected for its ability to grow with L-serine as sole carbon source, the rbl-1::Tn10 mutant had high levels of L-serine deaminase activity (due to increased transcription of the structural gene) and of another amino acid-degrading enzyme, L-threonine dehydrogenase, and decreased transcription of the operons serA and ilvIH, coding for biosynthetic enzymes. The rbl mutation suppressed the slow growth of a metK mutant, deficient in S-adenosylmethionine synthetase. Furthermore, metK mutants spontaneously accumulated faster-growing rbl-like derivatives, and a commonly used metK strain, RG62, carries such a mutation. The rbl gene is located near 20 min on the E. coli genetic map. All phenotypes of the rbl mutant could be observed in rbl+ strains cultivated in the presence of L-leucine, and exogenous L-leucine had little further effect on the rbl strains. We propose that the rbl gene product is the regulator of a global response to leucine.

Isolation and characterization of nitrogenase-derepressed mutant strains of cyanobacterium Anabaena variabilis

A positive selection method for isolation of nitrogenase-derepressed mutant strains of a filamentous cyanobacterium, Anabaena variabilis, is described. Mutant strains that are resistant to a glutamate analog, L-methionine-D,L-sulfoximine, were screened for their ability to produce and excrete NH4+ into medium. Mutant strains capable of producing nitrogenase in the presence of NH4+ were selected from a population of NH4+-excreting mutants. One of the mutant strains (SA-1) studied in detail was found to be a conditional glutamine auxotroph requiring glutamine for growth in media containing N2, NO3-, or low concentrations of NH4+ (less than 0.5 mM). This glutamine requirement is a consequence of a block in the assimilation of NH4+ produced by an enzyme system like nitrogenase. Glutamate and aspartate failed to substitute for glutamine because of a defect in the transport and utilization of these amino acids. Strain SA-1 assimilated NH4+ when the concentration in the medium reached about 0.5 mM, and under these conditions the growth rate was similar to that of the parent. Mutant strain SA-1 produced L-methionine-D,L-sulfoximine-resistant glutamine synthetase activity. Kinetic properties of the enzyme from the parent and mutant were similar. Mutant strain SA-1 can potentially serve as a source of fertilizer nitrogen to support growth of crop plants, since the NH4+ produced by nitrogenase, utilizing sunlight and water as sources of energy and reductant, respectively, is excreted into the environment.

Escherichia coli K-12 lysyl-tRNA synthetase mutant with a novel reversion pattern

Fast-growing revertants have been selected from a slow-growing lysyl-tRNA synthetase mutant. All of the revertants had increased lysyl-tRNA synthetase activity compared with the mutant (5- to 85-fold), and in some revertants this amounted to two to three times the wild-type synthetase activity. Two-dimensional gel electrophoresis of a whole-cell extract of revertant IH2018 (1.5- to 2-fold wild-type synthetase activity) showed that the increase in synthetase activity is due to the induction of cryptic lysyl-tRNA synthetase forms and not to a change in the constitutive lysyl-tRNA synthetase. Genetic studies have shown that a locus termed rlu (for regulation of lysU ) which is cotransducible with purF at 49.5 min influences the amount of the cryptic lysyl-tRNA synthetase.

Physical organization of the metJB component of the Escherichia coli K-12 metJBLF gene cluster

The structures of a series of plaque-forming metJB transducing phage were studied by restriction endonuclease mapping and enzyme activity assay. One of these phage, lambda pmet100, was inactivated by heat shock in the presence of EDTA, and deletion mutants were selected from the survivors. Two of these mutants, lambda pmet100 delta 1 and lambda pmet100 delta 2, were used to confirm the gene order metJ metB when moving clockwise on the linkage map of Escherichia coli K-12. Additional results indicate that the metB gene can be expressed independently of any other component of the met regulon and that the metJ gene also forms a separate transcription unit.

Mutagenesis of the metJBLF gene cluster with transposon Tn5: localization of the metF transcription unit

Mutants of a specialized lambda dmet transducing phage bearing the metJBLF gene cluster of Escherichia coli K12 were constructed using transposon Tn5. Two of these mutants, lambda dmet128::Tn5, MW77 and lambda dmet128::Tn5, 3-1, were used to locate precisely as well as confirm the existence of the metF transcription unit (approximately 1,000 base pairs in size). The introduction of new restriction sites within the metJBLF gene cluster due to the Tn5 insertion events allowed the metF transcription unit to be cloned into the high copy number plasmid pBR322. Analyses of the structures of two of these recombinant plasmids, pTJ77H and pTJ13-1H, are presented. Expression of the plasmid borne metF allele in cells grown in the absence, or presence, of exogenous L methionine (0.2 mM) demonstrates that the amplification of the metF copy number does not abolish met regulon mediated control of the gene's activity.