Transcriptional regulation of the proC gene of Salmonella typhimurium

We found that the expression of beta-galactosidase in Salmonella typhimurium strains carrying proC-lacZ fusions was neither repressed by excess proline nor derepressed by proline limitation. Except for a three- to fourfold decrease in the beta-galactosidase specific activity under conditions causing a severely reduced growth rate, the expression of the proC-lacZ fusions was nearly invariant under a variety of culture conditions. Thus, the proC gene is unlike most other amino acid biosynthetic genes in that its expression is nearly constitutive.     

Hydrogen production by Escherichia coli containing a cloned hydrogenase gene from Citrobacter freundii

Two hydrogenase genes of Citrobacter freundii complementing different Escherichia coli hyd mutations were cloned on the multicopy-plasmid pBR322. Recombinant plasmids pCBH2 and pCFH1 were obtained. Since hydrogenase activities of E. coli transformant HK-8 (pCBH2) and HK-7 (pCFH1) were much the same as E. coli C600 (wild type cells), the reduction in DNA size of recombinant plasmid pCBH2 (10.7 kb) was investigated. Reduced recombinant plasmids pCBH4 (6.2 kb) and pCBH6 (5.7 kb) were obtained, and a hydrogenase gene was found to be located on the 2.35 kb fragment between AvaI and EcoRI sites. Hydrogenase activity and hydrogen-evolving activity of E. coli HK-8 (pCBH4 or pCBH6) from sodium formate, sodium pyruvate or glucose were approximately 2-fold higher than those of E. coli C600 (wild type cells).On the other hand, a reduced recombinant plasmid pCBH10 (6.0 kb), which contained the adjacent DNA fragment (2.15 kb) to a hydrogenase gene, was obtained. Hydrogenase activity of E. coli C600 harboring pCBH10 was half that of E. coli C600. From these results we estimate that in plasmid pCBH2, the repressor gene suppressing the synthesis of hydrogenase might have been cloned together with a hydrogenase gene.     

Cloning and expression of Citrobacter freundii hydrogenase genes in Escherichia coli

Summary Escherichia coli mutants deficient in hydrogenase activity (Hyd^-) were derived from E. coli C600 by mutagenesis with nitrosoguanidine. Hydrogenase activities of mutant strains; HK-2, HK-7, HK-8, HK-16, HK-23, and HK-26 were below 1/100 that of the parental strain E. coli C600. Conjugational transfer of plasmid F-143 to the mutants was carried out and hydrogenase activities of the transformants were assayed. Recovery of hydrogenase activities in mutant strains; HK-2, HK-7, HK-8, HK-16, and HK-23 was observed, but not for HK-26. Two kinds of hydrogenase genes of Citrobacter freundii were cloned on pBR 322 and hybrid plasmids pCBH2 and pCFH1 were obtained. Hydrogenase activities of mutant strains HK-2, HK-8 and HK-16 were complemented with pCBH2 and strain HK-7 with pCFH1 respectively. The other mutant strains, HK-23, HK-26, however, were not complemented with these plasmids.     

Expression of the hut operons of Salmonella typhimurium in Klebsiella aerogenes and in Escherichia coli.

The normal hut (histidine utilization) operons, as well as those with mutations affecting the regulation of their expression, of Salmonella typhimurium were introduced on an F' episome into cells of S. typhimurium and Klebsiella aerogenes whose chromosomal hut genes had been deleted and into cells of Escherichia coli, whose chromosome does not carry hut genes. The episomal hut operons respond in a manner very similar to induction and catabolite repression in all three organisms. The small differences found reflect both different abilities to take up inducers from the medium and different degrees of catabolite repression exerted by glucose.     

Metabolic regulation of the histidine operon in Escherichia coli and Salmonella typhimurium

Expression of the histidine operon in Escherichia coli cells in contrast to the one in Salmonella typhimurium is changed proportionally to cells growth rate on the different carbon sources. The specific activity of histidinol-dehydrogenase is repressed by addition of 19 amino acids both in Escherichia coli and Salmonella typhimurium independent of the growth medium used. Using of Escherichia coli and Salmonella typhimurium strains containing the heterologous histidine operons made possible to demonstrate the dependence of the histidine operon metabolic regulation to be determined by the operon itself but not by the specificity of the recipient cells. ppGpp was shown to be a positive regulator of the histidine operon expression in Escherichia coli.     

Tryptophan-requiring parental strains yield Salmonella typhimurium x Escherichia coli hybrid recombinants with functional tryptophan operons.

Crosses between an Escherichia coli Hfr trp strain and three Salmonella typhimurium F- trp strains produced some trp+ hybrids in which the tryptophan operon is composed of genes from both parental species.     

弗氏柠檬酸菌甘油脱水酶基因在大肠杆菌中的克隆和表达

以弗氏柠檬酸菌（Citrobacter freundii）基因组DNA为模板,通过PCR得到甘油脱水酶（glycerol dehydratase）基因dhaB、dhaC、dhaE,克隆到表达载体pSE380上,得到重组质粒pSn-dhaBCE。将此重组质粒转化到E．coli JM109中,重组菌株SDS-PAGE结果显示有明显的61kD、22kD、16kD三条特异性蛋白条带出现。重组菌株经诱导表达,酶活力为11．59U／mL。     

Nucleotide sequence of the trpB gene in Escherichia coli and Salmonella typhimurium

We have obtained the entire nucleotide sequence of the penultimate gene of the tryptophan operon, trpB, in Escherichia coli and Salmonella typhimurium. The amino acid sequence deduced for the E. coli gene product is in agreement with earlier, fragmentary protein sequence results. The trpB nucleotide sequences for the two bacterial species are perfectly colinear and show 85% identity. Most of the nucleotide differences found are without consequence for the amino acid sequence, which shows greater than 96% identity. The degree of conservation of both the nucleotide and amino acid sequences is significantly greater than for trpA, the adjacent gene encoding the other subunit of the same enzyme. When synonymous third codon position nucleotide differences are examined, they seem to be distributed at random throughout trpB and trpA, except for one completely conserved 66 basepair long region within trpB.     

The araC gene of Citrobacter freundii

The araC gene of Citrobacter freundii was cloned into plasmid pBR322 and expressed in Escherichia coli and Salmonella typhimurium. The nucleotide sequence and the predicted translational product were determined and compared to those of E. coli, S. typhimurium and Erwinia carotovora. The predicted translational product is 281 amino acids (aa) long, identical in size to that of S. typhimurium, and is 11 and 29 aa shorter than that of E. coli and E. carotovora, respectively. The nucleotide sequence of the araC gene of C. freundii is 83% homologous to the araC genes of both E. coli and S. typhimurium, but only 60% homologous to that of E. carotovora with respect to the regions they share. The predicted amino acid sequence is highly conserved and shows 96% and 94% homology to S. typhimurium and E. coli, respectively. E. carotovora shows only a 58% aa homology. The activator and autoregulatory activities of each plasmid encoded AraC protein in a S. typhimurium araC::lacZ protein fusion strain were examined.     

Nucleotide sequence of the Escherichia coli hisD gene and of the Escherichia coli and Salmonella typhimurium hisIE region

Summary In this paper we report the nucleotide sequence of the hisD gene of Escherichia coli and of the hisIE region of both E. coli and Salmonella typhimurium. The hisD gene codes for a bifunctional enzyme, l-histidinol: NAD⁺ oxidoreductase, of 434 amino acids with a molecular mass of 46,199 daltons. We established that the hisIE region of both S. typhimurium and E. coli is composed of a single gene and not, as previously believed, of two separate genes. The derived amino acid sequence indicates that the hisIE gene codes for a bifunctional protein of 203 amino acids with an approximate molecular mass of 22,700 daltons. We also determined the nucleotide sequence of a deletion mutant in S. typhimurium which abolishes the hisF and hisI functions but retains the hisE function. We deduced that the mutant produces a chimeric protein fusing the aminoterminal region of the upstream hisF gene to the carboxylterminal domain of the hisIE gene which encodes for the hisE function. In view of these results the structural and functional organization of the histidine operon in enteric bacteria needs to be revised. The operon is composed of only 8 genes and the pathway leading to the biosynthesis of the amino acid requires 11 enzymatic steps.     

Peptidases and proteases of Escherichia coli and Salmonella typhimurium

A number of peptidases and proteases have been identified in Escherichia coli. Although their specific physiological roles are often not known, some of them have been shown to be involved in: the maturation of nascent polypeptide chains; the maturation of protein precursors; the signal peptide processing of exported proteins; the degradation of abnormal proteins; the use of small peptides as nutrients; the degradation of colicins; viral morphogenesis; the inactivation of some regulatory proteins for which a limited lifetime is a physiological necessity. Some of these enzymes act in concert to carry out specific functions. At present, twelve peptidases and seventeen proteases have been characterized. The specificity for only a few of them is known. The possible roles and the properties of these enzymes are discussed in this review.     

Fertility of Salmonella typhimurium Crosses with Escherichia coli

At least one factor that causes low fertility of Salmonella typhimurium LT2 strains in crosses with Escherichia coli K-12 Hfr's can be inhibited by growing the female strains in supplemented minimal salts medium rather than in nutrient broth and by incubating the female strains at 50 C immediately before mating with the Hfr. These pretreatments can enhance the recovery of prototrophic recombinants for markers injected early by the Hfr by a factor of as much as 10(4). The heat treatment is effective only on the female in intergeneric crosses and gradually loses (within 50 min) its effectiveness after return of heat-treated cells to 37 C. It is concluded that the restriction system of the female is heat-sensitive. Since markers injected late by the male enter females in which the heat-impaired restriction system has recovered, few recombinants for late markers are found. The presence of the leading end of an E. coli Hfr in an S. typhimurium-E. coli hybrid enhances by up to sevenfold the frequency of lac(+) recombinants in subsequent crosses with an E. coli Hfr if the E. coli segment is integrated into the chromosome of the hybrid; the effect is less marked if the E. coli segment is not integrated.