pACYC184-derived cloning vectors containing the multiple cloning site and lacZ alpha reporter gene of pUC8/9 and pUC18/19 plasmids

New shuttle vectors for Haemophilus influenzae and Escherichia coli: P15A-derived plasmids replicate in H. influenzae Rd

With the aim of identifying new plasmids useful for molecular cloning in Haemophilus influenzae, several P15A-derived plasmids were tested for their ability to transform H. influenzae Rd. The four plasmids tested, pACYC177, pACYC184, pSU2718, and pSU2719 were all able to establish in H. influenzae Rd. The plasmids were stable, could be purified by standard protocols, and were compatible with a plasmid carrying the RSF0885 origin of replication.

Genetic interaction between the beta' subunit of RNA polymerase and the arginine-rich domain of Escherichia coli nusA protein

The nusA11 mutation causes reduced transcription termination and temperature-sensitive growth of Escherichia coli. Suppressor mutations that restored growth of nusA11 mutant cells were isolated and named sna mutations. The intergenic suppressor mutation sna-10 was located in the rpoC gene at 90 min, which encodes the beta' subunit of RNA polymerase. sna-10 complemented the defect in tR1 termination caused by nusA11 and by itself stimulated termination of transcription at the lambda tR1 terminator. sna-10 is specific to the nusA11 allele and unable to suppress cold-sensitive growth of the nusA10 mutant. nusA10 carried two base substitutions at positions 311 and 634, causing two amino acid changes from the wild-type sequence. During these studies, we found three -1 frameshift errors in the wild-type nusA sequence; the correct sequence was confirmed by the peptide sequence and gene fusion analyses. The revised sequence revealed that nusA1 and nusA11 are located in an arginine-rich peptide region and substitute arginine and aspartate for leucine 183 and glycine 181, respectively. The intragenic suppressor study indicated that the nusA11 mutation can be suppressed by changing the mutated aspartate 181 to alanine or changing aspartate 84 to tyrosine.

Escherichia-Pseudomonas shuttle vectors derived from pUC18/19

Two new broad-host-range plasmid vectors, pUCP18 and pUCP19, which are stably maintained in Escherichia coli and Pseudomonas aeruginosa have been constructed. The plasmids are based on the E. coli pUC18 and pUC19 vectors and possess all their features: (i) convenient direct screening of recombinants; (ii) versatile multiple cloning site; (iii) use as sequencing and expression vectors; (iv) small size; and (v) intermediate to high copy number.

Iron(III) hydroxamate transport across the cytoplasmic membrane of Escherichia coli

Transport of iron(III) hydroxamates across the inner membrane into the cytoplasm of Escherichia coli is mediated by the FhuC, FhuD and FhuB proteins and displays characteristics typical of a periplasmic-binding-protein-dependent transport mechanism. In contrast to the highly specific receptor proteins in the outer membrane, at least six different siderophores of the hydroxamate type and the antibiotic albomycin are accepted as substrates. A fhuB mutant (deficient in transport of substrates across the inner membrane) which overproduced the periplasmic FhuD 30-kDa protein, bound [55Fe] iron(III) ferrichrome. Resistance of FhuD to proteinase K in the presence of ferrichrome, aerobactin, and coprogen indicated binding of these substrates to FhuD. FhuD displays significant similarity to the periplasmic FecB, FepB, and BtuE proteins. The extremely hydrophobic FhuB 70-kDa protein is located in the cytoplasmic membrane and consists of two apparently duplicated halves. The N- and C-terminal halves [FhuB(N) and FhuB(C)] were expressed separately in fhuB mutants. Only combinations of FhuB(N) and FhuB(C) polypeptides restored sensitivity to albomycin and growth on iron hydroxamate as a sole iron source, indicating that both halves of FhuB were essential for substrate translocation and that they combined to form an active permease. In addition, a FhuB derivative with a large internal duplication of 271 amino acids was found to be transport-active, indicating that the extra portion did not disturb proper insertion of the active FhuB segments into the cytoplasmic membrane. A region of considerable similarity, present twice in FhuB, was identified near the C-terminus of 20 analyzed hydrophobic proteins of periplasmic-binding-protein-dependent systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of the Citrobacter freundii group I beta-lactamase in Escherichia coli is not dependent on entry of beta-lactam into the cytoplasm

Induction of the cloned ampC Citrobacter freundii beta-lactamase in Escherichia coli by 6-aminopenicillanic acid was prevented by periplasmic TEM beta-lactamase in the same cell. In contrast, cytoplasmic TEM beta-lactamase did not prevent induction. This result implies that entry of the beta-lactam into the cytoplasm is not necessary for induction of ampC.

Iron(III) hydroxamate transport of Escherichia coli: restoration of iron supply by coexpression of the N- and C-terminal halves of the cytoplasmic membrane protein FhuB cloned on separate plasmids

Transport of iron(III) hydroxamates across the inner membrane into the cytoplasm of Escherichia coli cells is mediated by the FhuC, FhuD and FhuB proteins. We studied the extremely hydrophobic FhuB protein (70 kDa) which is located in the cytoplasmic membrane. The N- and C-terminal halves of the protein [FhuB(N) and FhuB(C)] show homology to each other and to the equivalent polypeptides involved in uptake of ferric dicitrate and of vitamin B12. Various plasmids carrying only one-half of the fhuB gene were expressed in fhuB- mutants. Only combinations of FhuB(N) and FhuB(C) polypeptides restored sensitivity to albomycin and growth on iron hydroxamates as sole iron source; no activity was obtained with either half of FhuB alone. These results indicate that both halves of FhuB are essential for substrate translocation and that they combine to form an active permease when expressed separately. In addition, a FhuB derivative with a large internal duplication of 271 amino acids was found to be partially active in transport, indicating that the extra portion did not perurb proper insertion of the active FhuB segments into the cytoplasmic membrane.

Isolation of the replication and partitioning regions of the Salmonella typhimurium virulence plasmid and stabilization of heterologous replicons

Although the virulence plasmid of Salmonella typhimurium has a copy number of one to two per chromosome, plasmid-free segregants are produced at a rate less than 10(-7) per cell per generation. Three regions appear to be involved in the maintenance of this virulence plasmid. The first two, repB and repC, are functional replicons hybridizing with IncFII and IncFI plasmids, respectively, neither exhibiting the segregational stability of the parent virulence plasmid. The third region, par, cloned as a 3.9-kilobase Sau3A fragment, is not a functional replicon but exhibits incompatibility with the virulence plasmid. Subsequent tests revealed the ability of this 3.9-kilobase par insert to increase the stability of pACYC184 in S. typhimurium from less than 34% to 99% plasmid-containing cells after 50 generations. In addition, the par region increased the stability of oriC, R388, and repC replicons in both S. typhimurium and Escherichia coli hosts. The par region encodes 44,000- and 40,000-molecular-weight proteins essential for the Par+ phenotype but not for the Inc+ phenotype. Although actual sequestering of plasmids within the cell was not demonstrated, all results indicate that the par region described is an actual partitioning locus, similar in organization to those described for plasmids F, P1, and NR1.

A highly efficient electroporation system for transformation of Yersinia

The various pathogenic Yersinia species are not readily and efficiently transformed by classical methods. For this reason, the electroporation technique was applied for genetic transformation of these species. Using optimal conditions, we were able to transform the six Yersinia strains studied with the two most widely used groups of plasmids: pSU2718 (a pACYC184 derivative) and pK19 (a pUC19 derivative). Only Yersinia enterocolitica (Y. e.) serotype 0:8 gave poor results (less than 5 x 10(2) transformants/microgram) DNA). Electrical transformation of the other species resulted in high efficiencies, up to 10(5) transformants/microgram DNA for Y. e. serotypes 0:3 and 0:9, 10(6) for Y. pseudotuberculosis and 10(7) for Y. pestis. The results varied for each strain with the type of plasmid used. Neither the introduced foreign plasmid nor the resident 72-kb virulence plasmid underwent detectable deletions. Transformation was most efficient with supercoiled DNA, decreasing by one and four orders of magnitude for relaxed circular and linearized plasmids, respectively. The ability to easily and efficiently transfer plasmid DNA via electroporation will greatly facilitate the application of recombinant DNA technology for direct cloning and analysis of significant genes into Yersinia.

Deletion-tolerance and trans-splicing of the bacteriophage T4 td intron. Analysis of the P6-L6a region

Non-directed mutagenesis and phylogenetic comparison suggest that certain elements of the bacteriophage T4 td group Ia intron are dispensable to self-splicing. The L6-P6a-L6a region was identified as a potential non-essential element, and was removed by sequential deletions extending from the L6a loop toward the P6 pairing. Assays for splicing indicate that as long as the P6 pairing is maintained, the 1016 nucleotide td intron can be reduced to less than 250 nucleotides while maintaining function in vivo and in vitro. The P6 pairing appears to be essential for splicing while P6a is not. In addition, a spontaneous pseudorevertant of a splicing-defective deletion was isolated and shown to result from a single nucleotide change in the predicted L6a loop. This genetic suppressor mimics the ability of Mg2+ to reverse the phenotype of the deletion, suggesting that function is restored by structural stabilization of P6. The tolerance of this region to deletion prompted us to split the ribozyme core in L6a, to generate precursors that might function in trans. Indeed, the two half-molecules do associate to form a bimolecular complex that yields accurately ligated exons both in vitro and in vivo. The biological implications of these results, as well as the usefulness of trans-splicing for generating unprocessed precursors in vitro are discussed.

Genetic analysis of an invasion region by use of a Tn3-lac transposon and identification of a second positive regulator gene, invE, for cell invasion of Shigella sonnei: significant homology of invE with ParB of plasmid P1

We have previously cloned two distinct regions of the Shigella sonnei form I plasmid pSS120, a 37-kilobase-pair DNA region and a virF region, which were found to be essential for cell invasion in Escherichia coli K-12 (J. Kato, K. Ito, A. Nakamura, and H. Watanabe, Infect. Immun. 57:1391-1398, 1989). The 37-kilobase-pair DNA region was randomly inserted by use of transposon Tn3-lac. At least eight genes were found to be located within the region, as determined by analysis of Tn3-lac-generated lac fusions. Expression of six genes, ipaB, ipaC, invE, invG, invJ, and invK, was apparently regulated by the positive regulator virF. IpaB and IpaC proteins could not found in invE mutants even if the virF gene was present. This observation suggested that the invE region encoded a positive regulator different from the virF gene. The functional relationship between the invE and virF genes was then examined. Translational fusions ipaB::Tn3-lac and invJ::Tn3-lac were used as indicators for gene expression, and the following results were obtained. Full expression of the ipaB and invJ genes required the presence of both the invE and virF regions. virF positively regulated the expression of invE at the transcriptional level. An increase in the copy number of invE enhanced the expression of ipaB and invJ in the absence of virF. These findings strongly indicate that the invE gene product, whose expression is regulated by virF, acts positively on the invasion-associated genes. InvE is a 35,407-dalton protein and has significant homologies with ParB of plasmid P1 and SopB of plasmid F, which are DNA-binding proteins involved in plasmid partitioning.

Proteolytic activity of the plum pox potyvirus NIa-protein on excess of natural and artificial substrates in Escherichia coli

The plum pox potyvirus (PPV) NIa protease expressed from a medium copy number plasmid was able to process an excess of substrate expressed from a high copy number plasmid, in a binary Escherichia coli expression system. The delta B7 NIa protease mutant only partially processed the NIb-CP junction but its efficiency was independent of the amount of substrate. The delta B7 mutant essentially did not recognize an artificial cleavage site which was quite efficiently recognized by the wild-type protease. No competitive inhibition of the proteolytic activity by the presence of excess of different protease mutants was observed.