Nucleotide sequence of the metH gene of Escherichia coli K-12 and comparison with that of Salmonella typhimurium LT2

The Escherichia coli K-12 metH gene, encoding the vitamin B12-dependent homocysteine transmethylase, is located between iclR and lysC in the 91-min region of the chromosome. The metH gene has been sequenced and reveals an open reading frame of 3600 bp encoding a polypeptide of 1200 amino acids (aa) with a calculated Mr of 132 628. The first 414 aa of the deduced polypeptide sequence are 92% identical to the 414 aa deduced from the partially sequenced Salmonella typhimurium LT2 metH gene. In-frame fusions of metH to lacZ were used to confirm the reading frame of the metH gene and to study its regulation. metH was repressed tenfold, presumably indirectly, by L-methionine and the metJ gene product, while vitamin B12 did not induce de novo synthesis of MetH.     

Stabilization of glucose-starved Escherichia coli K12 and Salmonella typhimurium LT2 by peptidase-deficient mutants

Escherichia coli K12 and Salmonella typhimurium LT2 cells were stabilized during carbon starvation in the presence of peptidase-deficient mutant strains. The rate of loss of viability of the wild-type S. typhimurium strain was decreased an average of 2-fold, and the rate for the wild-type E. coli strain was decreased about 2.3-fold, when either was starved in the presence of the multiply peptidase-deficient S. typhimurium strain TN852; other peptidase-deficient strains exhibited similar stabilizing effects. Starving wild-type S. typhimurium LT2 cells utilized peptides excreted by the starving peptidase-deficient cells for protein synthesis, and, to a lesser extent, as respiratory substrates. Provision of free amino acids in steady-state levels to starving E. coli K12 cells in a cell recycle apparatus had a stabilizing effect similar to that of mixing with peptidase-deficient cells.     

Sample sequencing of a Salmonella typhimurium LT2 lambda library: comparison to the Escherichia coli K12 genome

As part of the ongoing sequencing of the complete Salmonella typhimurium LT2 genome, a partly ordered set of 416 lambda clones has been developed, representing over 90% of the genome. The average insert size is 17 kb. Sequences were obtained from both ends of each clone in this set. A total of over 600 kb of sequence has been deposited in the genome survey sequence section of GenBank. This resource of clones is available from the Salmonella Genome Stock Center. A preliminary comparison with the Escherichia coli K12 genome indicates that there are likely to be many hundred insertion deletion events, encompassing more than one gene, that distinguish these genomes. Fully 30% of the S. typhimurium sequences have no close homologs in the GenBank database.     

Genetic Transfer of Salmonella typhimurium and Escherichia coli Lipopolysaccharide Antigens to Escherichia coli K-12

Escherichia coli K-12 varkappa971 was crossed with a smooth Salmonella typhimurium donor, HfrK6, which transfers early the ilv-linked rfa region determining lipopolysaccharide (LPS) core structure. Two ilv(+) hybrids differing in their response to the LPS-specific phages FO and C21 were then crossed with S. typhimurium HfrK9, which transfers early the rfb gene cluster determining O repeat unit structure. Most recombinants selected for his(+) (near rfb) were agglutinated by Salmonella factor 4 antiserum. Transfer of an F' factor (FS400) carrying the rfb-his region of S. typhimurium to the same two ilv(+) hybrids gave similar results. LPS extracted from two ilv(+),his(+), factor 4-positive hybrids contained abequose, the immunodominant sugar for factor 4 specificity. By contrast, his(+) hybrids obtained from varkappa971 itself by similar HfrK9 and F'FS400 crosses were not agglutinated by factor 4 antiserum, indicating that the parental E. coli varkappa971 does not have the capacity to attach Salmonella O repeat units to its LPS core. It is concluded that the Salmonella rfb genes are expressed only in E. coli varkappa971 hybrids which have also acquired ilv-linked genes (presumably rfa genes affecting core structure or O-translocase ability, or both) from a S. typhimurium donor. When E. coli varkappa971 was crossed with a smooth E. coli donor, Hfr59, of serotype O8, which transfers his early, most his(+) recombinants were agglutinated by E. coli O8 antiserum and lysed by the O8-specific phage, Omega8. This suggests that, although the parental E. coli K-12 strain varkappa971 cannot attach Salmonella-specific repeat units to its LPS core, it does have the capacity to attach E. coli O8-specific repeat units.     

Structural Genes for Ornithine Transcarbamylase in Salmonella typhimurium and Escherichia coli K-12

Mutations of Salmonella typhimurium affecting the structural gene for ornithine transcarbamylase (argl) have been isolated and mapped. The two ornithine transcarbamylase loci in Escherichia coli K-12 have been demonstrated by F′ episome transfer.     

Control of arg gene expression in Salmonella typhimurium by the arginine repressor from Escherichia coli K-12

Summary The regulation of synthesis of arg enzymes in Salmonella typhimurium by the arginine repressor of Escherichia coli K-12 has been reevaluated using a strain of S. typhimurium in which the argR gene was rendered nonfunctional by inserting the translocatable tetracyclineresistance element Tn10 into the argR gene. In contrast to previous studies, the introduction of the argR ⁺ allelle of E. coli on an F-prime factor to the argR::Tn10 S. typhimurium strain reduced the synthesis of arg enzymes to essentially wild-type levels. The elevated levels of arg enzymes observed in other hybrid merodiploids may have been the consequence of the formation of hybrid repressor molecules. The readily scoreable phenotype of tetracycline resistance facilitated establishing linkage of cod and argR (0.6% cotransduction) by P22 phage-mediated transduction.     

Comparative study of R1-specific chromosomal transfer in Escherichia coli K-12 and salmonella typhimurium LT2.

High-frequency transfer of the chromosomal trp region by R1 observed in Escherichia coli (Pearce and Meynell, 1968) also occurs in Salmonella typhimurium. The reaction is recA independent in both species. The origin of transfer lies within a segment of the chromosome that is inverted in S. typhimurium relative to E. coli, and thus transfer occurs in a different direction in the two species. The character of R1 that is responsible, known as Tfa+, may be lost without affecting other properties of the R factor such as its own transfer.     

The Salmonella typhimurium LT2 uvrD gene is regulated by the lexA gene product.

The uvrD gene product apparently plays a role in the repair of UV damage, in mismatch repair, and in genetic recombination. A lower level of expression of the Salmonella typhimurium LT2 uvrD gene was observed in maxicells prepared from an Escherichia coli strain that contained a lexA+ plasmid than in maxicells prepared from an E. coli strain that lacked functional LexA protein. These results suggest that the uvrD+ gene is repressed by the LexA protein and is thus a member of the set of genes whose expression is increased by "SOS"-inducing treatments.     

The EnvZ protein of Salmonella typhimurium LT-2 and Escherichia coli K-12 is located in the cytoplasmic membrane

Abstract The osmoregulated expression of the porin proteins OmpC and OmpF in S. typhimurium and E. coli is dependent on the regulatory proteins OmpR and EnvZ. The function of the EnvZ protein is not clear. In order to establish the cellular location of EnvZ two different methods of buoyant sucrose density centrifugation was employed. The presence of EnvZ in the different fractions was visualised by immunoblotting. It was conclusively shown that the EnvZ protein is located in the cytoplasmic membrane fraction. The result is in agreement with the available sequence data which shows that the EnvZ polypeptide contains two long hydrophobic stretches.