Construction and analysis of miniplasmids of the colicin Ib plasmid

Plasmid Co1IB contains an ssi signal close to the replication origin

Taking advantage of the plaque morphology method, we identified a single-strand initiation (ssi) signal in plasmid pSM32, a mini-Co1Ib plasmid. This ssi signal was situated in the 350-nt HaeIII segment of the 1.8-kb S7 fragment, and located nearly 400 nt downstream of the origin of DNA replication. Introduction of the ssi signal into a mutant of filamentous phage M13 lacking oric resulted in restoration of phage growth and RFI DNA synthesis. Interestingly, DNA homology studies showed that the nucleotide sequence of the ssi signal was extremely homologous with that of the "G4-type" ssi signal in plasmid R100.

ColIb plasmid genes that inhibit the replication of T5 and T7 bacteriophage

The colicin Ib (ColIb) plasmid genes that inhibit the replication of the T5-like and T7 bacteriophage have been cloned on an approximately 7200-bp ClaI fragment and their sites relative to each other and to the colicin immunity (imm) gene have been mapped. The inhibition of wild-type T7 by the clone is shown to be caused by the same gene or genes (pic) that cause the inhibition of T7 kinase-negative mutants and is a different gene than the one that causes inhibition of T5 (ibf or abi). The pic gene does not hybridize to the pif genes of the F plasmid that also cause the replication of T7 to be inhibited. The abi gene and the pic gene map very closely together but are under the control of different promoters. The abi gene has a maximum size of 900 bp and lies approximately 3000 bp away from the immunity gene, distal to the colicin gene. A site which maps in or near the gene binds very tightly to Escherichia coli RNA polymerase. The pic gene or genes lie between the abi gene and the imm gene and are contiguous with abi. Promoters for pic have been mapped and hypotheses to explain the inhibition of T7 by a cloned gene but not the whole ColIb plasmid are presented.

Organization and regulation of the conjugation genes of IncI1 plasmid colIb-P9

The IncI1 plasmid ColIb-P9 is among a group of related plasmids that encode the I1 type of conjugation system. The I1 system is known to include two morphologically distinct types of pilus, a DNA primase gene (sog) and an exclusion determinant (exc). Transposon mutagenesis and analysis of cloned fragments of ColIb were used to identify the location of these determinants with respect to an EcoRI restriction map. Also identified were the location of the origin of transfer (oriT) and a gene determining an EDTA-resistant nuclease, which is coordinately regulated with the transfer genes. The results indicate that the ColIb tra genes are separated into at least three Tra regions. The pleiotropic nature of transposon insertion mutations in two of these regions suggests that two positive regulators are required for expression of the transfer genes and evidence is also found for a trans-acting repressor. It is suggested that the I1 conjugation system may have evolved following fusion of two distinct types of conjugative plasmid.

Characterization of self-transmissible plasmids determining lactose fermentation and multiple antibiotic resistance in clinical strains of Klebsiella pneumoniae

The lactose fermentation (Lac+) and antibiotic resistance (R+) phenotypes were conjugally transferred from Klebsiella pneumoniae strains (K166, K182, K186, K218, and K220) to Salmonella typhi, S. typhimurium, Shigella flexneri, and Vibrio cholerae. The genes for lactose fermentation and antibiotic resistance were located on the plasmids. Further analysis of plasmid DNA from these isolates indicated the presence of multiple plasmids (Mr ranged less than 2.7 to 70 X 10(6)). The Lac+R+ plasmids p166 and p182 were members of the FII incompatibility group. The fertility inhibition property of plasmids, p182, p218, and p220 was fi+ type. Furthermore, phage typing experiments showed that plasmids p166 and p218 (Lac+R+) conferred the ability to inhibit the multiplication of bacteriophages 12 and 13 in S. typhimurium. However, the plasmids p182, p186, and p220 (Lac+R+) could inhibit the visible lysis of all the 30 phages in S. typhimurium. This study describes the characterization of Lac+R+ plasmids and the medical significance of an intergeneric transfer of lactose fermentation to non-lactose-fermenting pathogens.

Poliovirus RNA-dependent RNA polymerase and host cell protein synthesize product RNA twice the size of poliovirion RNA in vitro

The poliovirus RNA-dependent RNA polymerase required an oligouridylate primer or a HeLa cell protein (host factor) to initiate RNA synthesis on poliovirion RNA in vitro. The polymerase synthesized template-sized product RNA in the oligouridylate-primed reaction. In the host factor-dependent reaction, the largest product RNA synthesized by the polymerase was twice the size of the template RNA. About half of the product RNA recovered from this reaction was shown to exist in the form of a snapback sequence. Time-course reactions and pulse-chase experiments showed that the product RNA was only slightly larger than the template RNA at early reaction times and that with time it increased in size to form the dimer-sized product RNA. Inhibition of the elongation reaction by adding only [alpha-32P]UTP and ATP resulted in the formation of template-sized product RNA. The dimer-sized product RNA was unaffected by phenol extraction or proteinase K treatment but was converted to template-sized molecules by S1 nuclease. Dimer-sized poliovirus RNA that was sensitive to S1 nuclease was also isolated from poliovirus-infected cells. The results from this study indicate that the labeled negative-strand product RNA synthesized in vitro was covalently linked to the positive-strand template RNA. Thus, in vitro, the primer-dependent poliovirus RNA polymerase may initiate RNA synthesis in the presence of the host factor by using the 3' end of the template RNA as a primer.

Physical and genetic characterization of the IncI plasmid R144-drd3

A physical and genetic map of the IncI plasmid R144-drd3 was obtained by determining restriction endonuclease sites and by physical and genetic analysis of cloned fragments, of Tn1 insertion mutants and of deletion mutants.