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P L Bergquist

Publications and source records attributed to P L Bergquist.

At least 73 records · Page 4Linked to original sources
PubMed1988

A replication region of the IncHI plasmid, R27, is highly homologous with the RepFIA replicon of F.

A region of the IncHI plasmid R27 has been found to share very close nucleotide sequence homology with the RepFIA replicon of F. This region has been located on a 1.6 kb segment of R27 plasmid DNA, and corresponds to ori-2 and the E gene of F. The incC repeat sequence region shows reduced homology, with the F repeats being an imperfect subset of a larger repeated sequence found in R27. The E gene homologue of R27 is able to initiate replication from the F ori-2 sequence and to repress the E gene promoter of F. The results are consistent with the observed incompatibility behaviour of R27, and have a bearing on the specificity of interaction of E protein with its DNA-binding sites.

Amino Acid Sequence↗
PubMed1987

Expression of leucine genes from an extremely thermophilic bacterium in Escherichia coli.

The organisation of the leucine genes in Thermus thermophilus HB8 was analysed by examining the ability of recombinant DNAs to complement Escherichia coli mutations. The arrangement of the genes is different from that in the mesophilic bacteria E. coli and Salmonella typhimurium. The promoter responsible for the expression of the leuB, leuC and leuD genes of Thermus HB8 in E. coli was identified. The sequence of Thermus DNA containing this promoter revealed structural similarities to the promoter and attenuator regions of the E. coli leucine operon.

3-Isopropylmalate Dehydrogenase↗
PubMed1987

Characterization of the maintenance functions of IncFIV plasmid R124.

The genetic arrangement of the regions involved in R124 replication and incompatibility have been located and their homology to the IncFI basic replicons has been assessed. We show that R124 has homology with all three basic replicons, RepFIA, RepFIB, and RepFIC, and that these regions, FIVA, RepFIVB, and RepFIVC, are widely separated on the R124 genome. Cloning of autonomously replicating fragments has shown that RepFIVB and RepFIVC are functional in R124 and express incompatibility. The FIVA region was unable to form a functional replicon and when cloned into pUC8 lacked incompatibility activity. A fourth region of R124 was identified, which although not essential for replication stabilized mini-R124 plasmid replication and exhibited incompatibility with R124. This region, designated IncIV, showed no homology to RepFIA, RepFIB, or RepFIC. Incompatibility expression of IncIV required only the EcoRI fragment E13 but the strength of the reaction was modified in the presence of other fragments. The replication and incompatibility properties of an R124 deletion derivative indicated that R124 can switch its replication to either RepFIVB or RepFIVC when in the presence of an incompatible plasmid. The ambiguous incompatibility reactions reported for R124 is a result of the expression of the two functional replicons, RepFIVB and RepFIVC, and that expressed by IncIV.

Chromosome Mapping↗
PubMed1987

Nucleotide sequence analysis of RepFIC, a basic replicon present in IncFI plasmids P307 and F, and its relation to the RepA replicon of IncFII plasmids.

RepFIC is a basic replicon of IncFI plasmid P307 which is located within a 3.09-kilobase SmaI fragment. The nucleotide sequence of this region has been determined and shown to be homologous with the RepFIIA replicon of IncFII plasmids. The two replicons share three homologous regions, HRI, HRII, and HRIII, which are flanked by two nonhomologous regions, NHRI and NHRII. A comparison of coding regions reveals that the two replicons have several features in common. RepFIC, like RepFIIA, codes for a repA2 protein with its amino-terminal codons in HRI and its carboxy-terminal codons in NHRI. Although the codons for the repA1 proteins are located in NHRII, the DNA region containing a putative promoter, ribosomal binding site, and initiation codons is located in HRII. This region also codes for an inc RNA. There are nine base-pair differences between the inc RNA of RepFIIA and that of RepFIC, and as a result, RepFIC and RepFIIA replicons are compatible. An EcoRI fragment from the F plasmid which shows homology with RepFIC of P307 has also been sequenced. This fragment contains only a portion of RepFIC, including the genes for the putative repA2 protein and inc RNA. The region coding for a putative repA1 protein is interrupted by the transposon Tn1000 and shows no homology with the repA1 region of RepFIIA and RepFIC of P307. Our comparative and structural analyses suggest that RepFIC and RepFIIA, although different, have a similar replication mechanism and thus can be assigned to the same replicon family, which we designate the RepFIIA family.

Base Sequence↗
PubMed1986

Distribution of basic replicons having homology with RepFIA, RepFIB, and RepFIC among IncF group plasmids.

Plasmids encoding F-like pili have been divided into groups on the basis of their incompatibility behavior. Three basic replicons have been recognized previously in the IncFI plasmid group and we have now examined their distribution in representative plasmids from 22 of the currently recognized incompatibility groups. The occurrence of these basic replicons was found to be rare outside of the IncF group, and significant hybridization was shown only for RepFIA to IncH1 and I group plasmids. Homology to the RepFIC basic replicon was found in all but one of the IncF group plasmids examined but RepFIA and RepFIB have a more restricted distribution. It appears likely that some plasmids carry vestiges of replicons which still express incompatibility but are incapable of replication. We suggest that evolutionary divergence among the plasmids of the IncF group has resulted from various genetic rearrangements among these basic replicons.

Cloning, Molecular↗
PubMed1985

Molecular homology and incompatibility relationships between F and IncH1 plasmids.

IncH1 plasmids and the F plasmid of Escherichia coli display one-way compatibility. An entering IncH1 plasmid is incompatible with a resident F plasmid, but is compatible when it is the resident plasmid. There is little molecular homology between IncH1 plasmids and the F plasmid. A single 5 MDal EcoRI restriction enzyme fragment from digests of several IncH1 plasmids hybridizes with probes constructed from the primary replication region of F. Homology can be demonstrated only with the gene for the essential replication protein of F (gene E), but the expression of incompatibility behaviour appears to be associated with the presence of the secondary replicon of the F plasmid. Thus R27 and F are compatible under growth conditions allowing replication and maintenance of F by the secondary replicon. However, a mutant F plasmid which lacks the secondary replicon of F is incompatible with R27 in both directions, irrespective of the growth conditions used.

DNA Restriction Enzymes↗
PubMed1984

RepFIC, a basic replicon of IncFI plasmids that has homology with a basic replicon of IncFII plasmids.

It was found that a DNA segment containing genes for autonomous replication and its control (basic replicon) present in the IncFI plasmid P307 has homology with RepA, a basic replicon present in IncFII plasmids. The basic replicon in P307 is referred to as RepFIC and the homologous basic replicon in IncFII plasmids is referred to as RepFIIA. In 11 other IncFI plasmids studied a region that has homology with RepFIC and RepFIIA was demonstrated. Thus, of the several basic replicons present in IncFI plasmids, RepFIC is evolutionarily related to a basic replicon of IncFII plasmids.

Base Sequence↗
PubMed1983

A cryptic plasmid from Shigella sonnei.

pNZ500 is a 1.5 kb cryptic plasmid from a Shigella sonnei isolate. It was introduced into Escherichia coli by cotransformation, where it is maintained at about 30 copies per chromosome equivalent. Hybridization studies show that pNZ500 exhibits a high level of sequence similarity to other 1.5 kb plasmids found in different S. sonnei isolates but shares no homology with larger S. sonnei plasmids. pNZ500 shares a small degree of sequence homology with pBR322 and with pAC184. The homology with pBR322 is restricted to sequences close to the ori-bom region of this plasmid. Nevertheless, pNZ500 maintenance in E. coli is not dependent on DNA polymerase I activity, and does depend on continuing protein synthesis. pNZ500 encodes two polypeptide gene products whose monomer molecular weights are 24500 and 18000. The examination of host cells for the expression of possible plasmid phenotypes revealed no differences between cells bearing pNZ500 and plasmidless cells.

Bacterial Proteins↗
PubMed1982

IncD, a genetic locus in F responsible for incompatibility with several plasmids of the IncFI group.

Cloning of mini-F DNA segments has led to the identification and mapping of a locus, incD, involved in incompatibility reactions with many IncFI plasmids. The cloned incD locus expressed incompatibility with F, R386, and six other IncFI plasmids but not with ColV3-K30 or pHH507 which lack sequence homology with the incD region. A sequence of 360 bp (48.66-49.02 FKB) was found to be sufficient for expression of incD incompatibility. Multicopy vectors containing incD are compatible with each other, but can be displaced by mini-F plasmids deleted for incD. These results indicate that incD-mediated incompatibility reactions require the presence of replication genes to which incD is normally linked. The degree of incompatibility exercised by incD is moderate compared with that of other inc loci in F, suggesting that incD is involved in an aspect of plasmid maintenance, such as partition, different from the functions of the other inc loci.

Bacteriocin Plasmids↗
PubMed1982

Effects of Tn5 insertion in the incD region on mini-F maintenance and polypeptide synthesis.

The gene coding for the 33,000 dalton protein (B protein) of the mini-F plasmid has been mapped by minicell polypeptide analysis to 47.3-48.2 Fkb. Transcription of the gene is initiated near 47.3 Fkb. Gene B mutants overproduce the 42,000 dalton protein (A protein) of mini-F. Insertions of Tn5 in the B gene and in the incD region cause instability of plasmid inheritance. Mini-F plasmids deleted for part of gene B are not maintained in the absence of the incD region. B protein and the incD region appear to interact in promoting mini-F maintenance.

Bacterial Proteins↗
PubMed1982

An Mr 29000 protein is essential for mini-F maintenance in E. coli.

Plasmids consisting of mini-F inserted into multicopy vectors were constructed. Derivatives of these hybrid replicons were isolated which contained the transposon Tn5. The polypeptides encoded by these plasmids were identified by Escherichia coli minicell analysis. We show that a previously unidentified polypeptide of 29000 Mr is encoded by the mini-F gene E between 45.1 and 46.2 F kb on the mini-F plasmid map, and that this coding sequence (E gene) is transcribed rightward. Hybrid plasmids carrying Tn5 inserted into the E gene are unable to replicate in a polA- strain. Hence the E protein is essential for mini-F replication. Mutations in the A and B genes of mini-F affect E gene expression, and the results suggest that E protein synthesis is stimulated by A protein.

Bacterial Proteins↗
PubMed1982

Molecular homology and incompatibility in the IncFI plasmid Group.

The usual grounds for the inclusion of a plasmid in a particular incompatibility group are its mutual incompatibility with a type plasmid of that group, and, in some cases, the demonstration of shared regions of specific homology, presumed to be related to DNA replication. We have found that some plasmids classified as IncFI on genetical grounds share no homology with the previously described incompatibility regions of F on the basis of hybridization of specific radioactive probes to restriction enzyme digests of DNA from these plasmids. Others show homology with some or all of the regions of the F plasmid that can express incompatibility. The incompatibility behaviour of these plasmids has been examined to determine the relationship between the possession of regions of homology and the expression of incompatibility. Three plasmids, ColV3-K30, pHH507 and Entp307, show homology only with the secondary replicon of F and appear to use sequences homologous with the secondary F replicon in their replication. The results are consistent with the propositions that some contemporary IncFI plasmids arose by the integration of several replicons, and, in general, the replicon not being used for replicon expresses its incompatibility, as does the replicon being used for replication. We conclude that incompatibility of two plasmids with F does not necessarily demonstrate relatedness of the plasmids to each other, and that inclusion within the IncFI group can result from the possession of any of several combinations of inc sequences.

Base Sequence↗
PubMed1981

Analysis of mini-F plasmid replication by transposition mutagenesis.

Derivatives of a mini-F plasmid in which Tn3 is inserted in F deoxyribonucleic acid were obtained, and the sites of insertion for 40 of the derivatives were mapped. Tn3 was found to insert at many sites within mini-F, but most insertions were within the 43.0- to 43.7-kilobase (kb), 44.2- to 44.7-kb, and 45.9- to 46.3-kb segments. Hence, these segments are unnecessary for mini-F replication. Most of the Tn3 derivatives were similar to their parent miniplasmid with respect to copy number, stability, and incompatibility. Insertions at 45.15 kb and near 46.0 kb caused a moderate disruption of copy number control, and insertion at 47.6 kb resulted in unstable maintenance. Deletion derivatives lacking deoxyribonucleic acid between 40.3 and 44.76 kb and between 45.92 and 49.4 kb were obtained. This observation suggests either that mini-F contains a third origin, in addition to those already reported to be at 42.6 and 44.4 kb, or that the reported position of the secondary origin, 44.4 kb, is incorrect and that this origin is between 44.76 and 45.92 kb.

Base Sequence↗