Expression of the Pseudomonas aeruginosa PAK pilin gene in Escherichia coli.

Pseudomonas aeruginosa is a piliated opportunistic pathogen. We have recently reported the cloning of the structural gene for the pilus protein, pilin, from P. aeruginosa PAK (B. L. Pasloske, B. B. Finlay, and W. Paranchych, FEBS Lett. 183:408-412, 1985), and in this paper we present evidence that this chimera (pBP001) expresses P. aeruginosa PAK pilin in Escherichia coli independent of a vector promoter. The strength of the promoter for the PAK pilin gene was assayed, and the cellular location of the pilin protein within E. coli was examined. This protein was present mainly in the inner membrane fraction both with and without its six-amino-acid leader sequence, but it was not assembled into pili.     

Two modes of excision repair in toluene-treated Escherichia coli.

In toluene-treated Escherichia coli incision breaks accumulate during post-irradiation incubation in the presence of adenosine 5'-triphosphate (ATP). It is shown that incised deoxyribonucleic acid (DNA) is converted to high-molecular-weight DNA during reincubation in the presence of the four deoxyribonucleoside triphosphates (dNTP's) and nicotinamide adenine dinucleotide (NAD). This restitution process is ATP independent and N-ethylmaleimide insensitive and takes place only in polA+ strains. It is defective in strains carrying a mutation in the 5' leads to 3' exonucleolytic activity associated with DNA polymerase I. Repair of accumulated incision breaks differs from repair in which all the steps of the excision repair process occur simultaneously or in rapid succession. The latter is observed if toluene-treated E. coli are incubated immediately after irradiation in the presence of the four dNTP's, NAD, and ATP. It is shown that under these conditions dimer excision occurs to a larger extent than during repair of accumulated incision breaks and that, except in strains defective in polynucleotide ligase, incision breaks do not accumulate. This consecutive mode of repair is detectable in polA+ strains and at low doses also in polA mutants.     

Identification of the glmU gene encoding N-acetylglucosamine-1-phosphate uridyltransferase in Escherichia coli.

The physiological properties of the EcoURF-1 open reading frame, which precedes the glmS gene at 84 min on the Escherichia coli chromosome (J. E. Walker, N. J. Gay, M. Saraste, and A. N. Eberle, Biochem. J. 224:799-815, 1984), were investigated. A thermosensitive conditional mutant in which the synthesis of the gene product was impaired at 43 degrees C was constructed. The inactivation of the gene in exponentially growing cells rapidly inhibited peptidoglycan synthesis. As a result, various alterations of cell shape were observed, and cell lysis finally occurred when the peptidoglycan content was 37% lower than that of normally growing cells. Analysis of the pools of peptidoglycan precursors revealed a large accumulation of N-acetylglucosamine-1-phosphate and the concomitant depletion of the pools of the seven peptidoglycan nucleotide precursors located downstream in the pathway, a result indicating that the mutational block was in the step leading from N-acetylglucosamine-1-phosphate and UTP to the formation of UDP-N-acetylglucosamine. In vitro assays showed that the overexpression of this gene in E. coli cells, directed by appropriate plasmids, led to a high overproduction (from 25- to 410-fold) of N-acetylglucosamine-1-phosphate uridyltransferase activity. This allowed us to purify this enzyme to homogeneity in only two chromatographic steps. The gene for this enzyme, which is essential for peptidoglycan and lipopolysaccharide biosyntheses, was designated glmU.     

Two regulatory fim genes, fimB and fimE, control the phase variation of type 1 fimbriae in Escherichia coli.

The expression of type 1 fimbriae in Escherichia coli is phase dependent, i.e. a cell is either completely fimbriated or bald. This phenomenon is due to the periodic inversion of a specific 300-bp DNA segment containing the promoter for the fimbrial subunit gene, fimA. The phase switch is controlled by the products of two regulatory genes, fimB and fimE, located upstream of fimA. The fimB and fimE proteins direct the phase switch into the 'on' and 'off' position, respectively. The DNA sequence of a 3000-bp region containing the two genes has been determined. The fimB and fimE proteins exhibit strong homology and have most likely originated by duplication of an ancestral gene. They are highly basic implying that they control the phase switch through interaction at the DNA level.     

Cloning and expression of the pilin gene of Pseudomonas aeruginosa PAK in Escherichia coli.

Many strains of Pseudomonas aeruginosa possess pili which have been implicated in the pathogenesis of the organism. This report presents the cloning and expression in Escherichia coli of the gene encoding the structural subunit of the pili of P. aeruginosa PAK. Total DNA from this strain was partially digested with Sau3A and inserted into the cloning vector pUC18. Recombinant E. coli clones were screened with oligonucleotide probes prepared from the constant region of the previously published amino acid sequence of the mature pilin subunit. Several positive clones were identified, and restriction maps were generated. Each clone contained an identical 1.1-kilobase HindIII fragment which hybridized to the oligonucleotide probes. Western blot analysis showed that all of the clones expressed small amounts of the P. aeruginosa pilin subunit, which has a molecular mass of ca. 18,000. This expression occurred independently of the orientation of the inserted DNA fragments in the cloning vector, indicating that synthesis was directed from an internal promoter. However, subclones containing the 1.1-kilobase HindIII fragment in a specific orientation produced an order of magnitude more of the pilin subunit. While the expressed pilin antigen was located in both the cytoplasmic and outer membrane fractions of E. coli, none appeared to be polymerized into a pilus structure.     

The expression of Pseudomonas aeruginosa PAK pilin gene mutants in Escherichia coli

Previous work has demonstrated the expression of the cloned pilin gene of Pseudomonas aeruginosa PAK within Escherichia coli and has pinpointed this protein's localization exclusively to the cytoplasmic membrane (Finlay et al., 1986). To define regions of the pilin subunit necessary for its stability and transport within E. coli, we constructed six mutants of the pilin gene and studied their expression and localization using a T7 promoter system. Two of the mutants have either a 4- or 8-amino-acid deletion at the N-terminus and both were stably expressed and transported primarily to the cytoplasmic membrane of E. coli. The other four mutants are C-terminal truncations having between 36 and 56 amino acids of the N-terminal region of the unprocessed pilin. Studies with these truncated mutants revealed that only the first 36 residues of the unprocessed pilin subunit were required for insertion into the E. coli membrane.     

Purification of the Escherichia coli type 1 pilin and minor pilus proteins and partial characterization of the adhesin protein.

Type 1 pili of Escherichia coli contain three integral minor proteins with apparent molecular weights (Mr) of 28,000 (28K protein), 16,500, and 14,500 attached to rods composed of Mr-17,000 pilin subunits (Hanson and Brinton, Nature [London] 322:265-268). We describe here an improvement on our earlier method of pilus purification, which gives higher yields and higher purity. Also reported are methods allowing fractionation of intact type 1 pili into rods of pure pilin and free minor proteins, as well as fractionation of the 28K tip adhesion protein from the 16.5K and 14.5K proteins. We have determined the amino acid composition and amino-terminal sequence of the adhesion protein. This sequence shows limited homology with the amino-terminal sequences of several E. coli pilins, including type 1.     

Horizontal transfer of CS1 pilin genes of enterotoxigenic Escherichia coli

CS1 is one of a limited number of serologically distinct pili found in enterotoxigenic Escherichia coli (ETEC) strains associated with disease in people. The genes for the CS1 pilus are on a large plasmid, pCoo. We show that pCoo is not self-transmissible, although our sequence determination for part of pCoo shows regions almost identical to those in the conjugative drug resistance plasmid R64. When we introduced R64 into a strain containing pCoo, we found that pCoo was transferred to a recipient strain in mating. Most of the transconjugant pCoo plasmids result from recombination with R64, leading to acquisition of functional copies of all of the R64 transfer genes. Temporary coresidence of the drug resistance plasmid R64 with pCoo leads to a permanent change in pCoo so that it is now self-transmissible. We conclude that when R64-like plasmids are transmitted to an ETEC strain containing pCoo, their recombination may allow for spread of the pCoo plasmid to other enteric bacteria.     

Genetic diversity of the gene cluster encoding longus, a type IV pilus of enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) strains produce a type IV pilus named Longus. We identified a 16-gene cluster involved in the biosynthesis of Longus that has 57 to 95% identity at the protein level to CFA/III, another type IV pilus of ETEC. Alleles of the Longus structural subunit gene lngA demonstrate a diversity of 12 to 19% at the protein level with strong positive selection for point replacements and horizontal transfer.     

Cloning and orientation of the gene encoding polynucleotide phosphorylase in Escherichia coli.

Mutations which affect the activity of polynucleotide phosphorylase (PNPase) map near 69 min on the bacterial chromosome. This region of the chromosome has been cloned by inserting the kanamycin-resistant transposon Tn5 near the argG and mtr loci at 68.5 min. Large SalI fragments of chromosomal DNA containing the Tn5 element were inserted into pBR322, and selection was made for kanamycin-resistant recombinant plasmids. Two of these plasmids were found to produce high levels of PNPase activity in both wild-type and host strains lacking PNPase activity. The pnp gene was further localized and subcloned on a 4.8 kilobase HindIII-EcoRI fragment. This fragment was shown to encode an 84,000-molecular weight protein which comigrated with purified PNPase during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The orientation of the pnp gene was determined by insertion of Tn5 into the 4.8 kilobase fragment cloned in pBR322. Some of the insertions had lost the ability to elevate the level of PNPase activity in the host bacterium. Restriction mapping of the positions of the Tn5 insertions and analysis of plasmid-encoded polypeptides in UV-irradiated maxi-cells indicated that the pnp gene is oriented in the counterclockwise direction on the bacterial chromosome.     

Nucleotide sequence of the hag gene encoding flagellin of Escherichia coli.

We determined the DNA sequence of the hag gene of Escherichia coli K-12 and deduced the primary structure of the flagellin consisting of 497 amino acid residues. Comparison of the amino acid sequence with those of other bacterial flagellins revealed a high homology in the NH2- and COOH-terminal regions.     

Isolation, sequence, and expression in Escherichia coli of the Pseudomonas sp. strain ACP gene encoding 1-aminocyclopropane-1-carboxylate deaminase.

Pseudomonas sp. strain ACP is capable of growth on 1-aminocyclopropane-1-carboxylate (ACC) as a nitrogen source owing to induction of the enzyme ACC deaminase and the subsequent conversion of ACC to alpha-ketobutyrate and ammonia (M. Honma, Agric. Biol. Chem. 49:567-571, 1985). The complete amino acid sequence of purified ACC deaminase was determined, and the sequence information was used to clone the ACC deaminase gene from a 6-kb EcoRI fragment of Pseudomonas sp. strain ACP DNA. DNA sequence analysis of an EcoRI-PstI subclone demonstrated an open reading frame (ORF) encoding a polypeptide with a deduced amino acid sequence identical to the protein sequence determined chemically and a predicted molecular mass of 36,674 Da. The ORF also contained an additional 72 bp of upstream sequence not predicted by the amino acid sequence. Escherichia coli minicells containing the 6-kb clone expressed a major polypeptide of the size expected for ACC deaminase which was reactive with ACC deaminase antiserum. Furthermore, a lacZ fusion with the ACC deaminase ORF resulted in the expression of active enzyme in E. coli. ACC is a key intermediate in the biosynthesis of ethylene in plants, and the use of the ACC deaminase gene to manipulate this pathway is discussed.     

The genetic determinant of adhesive function in type 1 fimbriae of Escherichia coli is distinct from the gene encoding the fimbrial subunit.

The role of type 1 fimbriae in the mannose-sensitive attachment of Escherichia coli to eucaryotic cells was investigated by deletion mutation analysis of a recombinant plasmid, pSH2, carrying the genetic information for the synthesis and expression of functional type 1 fimbriae. A mutant, pUT2002, containing a deletion remote from the structural gene encoding the 17-kilodalton subunit protein of type 1 fimbriae failed to agglutinate guinea pig erythrocytes even though the bacteria expressed fimbriae morphologically and antigenically indistinguishable from those produced by the intact recombinant plasmid. Fimbriae isolated from pUT2002 failed to agglutinate guinea pig erythrocytes, but reacted with a monoclonal antibody specific for quaternary structural determinants of type 1 fimbriae. Moreover, the dissociated fimbrial subunits from this mutant were indistinguishable from normal fimbriae by their migration during electrophoresis in sodium dodecyl sulfate-polyacrylamide gels, by their reactivity with a monoclonal antibody directed against a subunit-specific epitope, and in enzyme-linked immunosorbent assays with monospecific antisera. These results indicate that the adhesive functions in type 1 fimbriae are dependent on a factor(s) encoded by a gene other than those required for synthesis, assembly, and expression of the structural 17-kilodalton subunit.     

Isolation and expression of the Escherichia coli gene encoding malate dehydrogenase.

An oligodeoxynucleotide specific for a pentapeptide sequence corresponding to amino acid residues 32 through 36 of Escherichia coli malate dehydrogenase was chemically synthesized and used to identify the mdh gene on plasmid pLC32-38 from the Clarke-Carbon recombinant library. Cells transformed with this plasmid exhibited a 10-fold increase in malate dehydrogenase activity. A 1.2-kilobase PvuII fragment which hybridized with the oligodeoxynucleotide probe was subcloned, and the identity of the mdh structural gene was confirmed by partial nucleotide sequence analysis. The expression of the mdh gene, as measured by both Northern blotting and enzyme assays, was found to vary over a 20-fold range with different culture conditions.