Cloning in Escherichia coli of genes involved in the synthesis of proline and leucine in Desulfovibrio desulfuricans Norway

Summary A library of Deusulfovibrio desulfuricans Norway genomic DNA was constructed in Escherichia coli with pBR322 as vector and plasmids able to complement the proA and leuB mutations of the host were screened. It was observed that all the plasmids studied were highly unstable, the insert DNA being rapidely lost under non-selective growth conditions. A 2.75 kb DNA fragment of D. desulfuricans Norway was found to complement E. coli ProA, ProB and ProC deficiencies. From the results of restriction analysis and Southern hybridization, it is proposed that the genes involved in proline and leucine biosynthesis are clustered on the chromosome of D. desulfuricans Norway.     

The plasmids of Acetobacter xylinum and their interaction with the host chromosome

Summary Acetobacter xylinum contains a complex system of plasmid DNA molecules. Plasmids of molecular weights or copy numbers different from the original wild-type, are found in different types of mutants. Restriction endonuclease digestion and DNA/DNA hybridization analysis, showed that the plasmids often contained partly, but not completely the same DNA sequences. Two of these plasmid classes were analysed in more detail, and could be shown to differ in size by about 5 kb. Hybridization analysis using cloned DNA fragments as probes, showed that sequences lacking in the smallest plasmid were still present in a DNA fraction co-migrating with linearized chromosomal DNA. In addition, at least part of the DNA in the smallest plasmid was present both in the plasmid and chromosomal DNA fraction. Analysis of a particular strain containing an insertion of transposon Tn1, also indicated the existence of complex interactions between plasmids and chromosomal DNA. Together with experiments on conjugative transfer and curing of the plasmids, the results indicate that at least part of the genetic system of A. xylinum is unusual when compared to that of other genetically characterized bacteria.     

Site-specific integration and excision of pMEA100 in Nocardia mediterranei

Summary Nocardia mediterranei strain LBG A3136 contains the 23.7 kb element pMEA100 in a chromosomally integrated form as well as in the free state (Moretti et al. 1985). The integrated form of this element can be excised precisely from the Nocardia chromosome without any accompanying rearrangements in flanking chromosomal DNA. After transfer into plasmid-free mutant strains, pMEA100 reintegrates site specifically into its original chromosomal locus. The exact mapping of the pMEA100 integration site was accomplished by restriction analysis and DNA sequencing. The attachment site of pMEA100, the junctions of its integrated form and plasmid-free chromosomal DNA of N. mediterranei contain an identical 47 bp long sequence which is probably required for site-specific recombination connected with integration and excision of pMEA100. Only one such sequence was found in the chromosome of pMEA100-free N. mediterranei derivatives as suggested by the single integration locus.     

Plasmid profiles and antibiotic susceptibility of Haemophilus pleuropneumoniae serotypes 1, 3, 5, and 7

Abstract This paper describes the plasmid profiles obtained for 73 of 96 field isolates of Haemophilus pleuropneumoniae serotypes 1, 3, 5, and 7. We also characterized the antibiotic susceptibilities of these 96 isolates. Because of the high proportion of isolates resistant to some of the antibiotics, no conclusions can be drawn as to the role of plasmids in antibiotic resistance.     

Specificity of the interactions between the Rep proteins and the origins of replication of Staphylococcus aureus plasmids pT181 and pC221

Summary pT181 and pC221 are closely relatedStaphylococcus aureus plasmids with the same genome organization, which is characterized by the overlapping of the origin of replication with the sequence encoding a protein, Rep, essential for plasmid replication. Former results have shown the lack of in vivo cross-complementation between these two plasmids, while in vitro studies have revealed the ability of both Rep proteins to act on either origin. One possible explanation for this difference was based on a previous analysis of the incompatibility expressed by the origin of replication of these plasmids, showing that the origin embedded in therep gene competes for Rep utilization with the origin of a test plasmid and that changes in the sequence of the origin reduce its ability to compete. To avoid this problem, in the present work special hybrids were constructed in which the origin of replication overlapping therep gene was mutationally inactivated, without changing the amino acid sequence of the encoded protein. The level of Rep expression by these hybrids could be varied by taking advantage of what is presently known about the control of Rep synthesis in plasmid pT181. The results of complenentation studies conducted using these hybrids have shown that: (i) at the usual level of expression for a wild-type plasmid each Rep protein can initiate replication strictly from its corresponding origin; (ii) when overproduced, the pT181 RepC protein could also act efficiently on the pC221 origin; a functional pT181 origin present in the same host completely prevented this complementation; (iii) in excess, the RepD protein encoded by pC221 could replicate a plasmid carrying the pT181 origin but could not ensure the hereditary stability of such a plasmid in the absence of another active replication system; (iv) when overproduced both RepC and RepD could act on the origin of replication of three other related plasmids pS194, pC223 and pUB112.     

Unusual genetic phenomena associated with Tn5 mutagenesis in Alcaligenes eutrophus strain H1

Tn5 was introduced into Alcaligenes eutrophus strain H1 by a suicide vector pSUP1011. Physical characterization of mutants obtained after Tn5 mutagenesis revealed a relatively high frequency of plasmid curing, or deletion of a 50 kb plasmid DNA segment. Results of Southern hybridization and chromosomal walking indicate that the same continuous stretch of plasmid DNA (designated as D region of plasmid) is deleted in four independent isolates. Moreover, the same deletion of plasmid DNA is also observed in a mitomycin C-generated mutant strain H1-4.Journal Paper No. J-12095 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 2607, supported in part by a grant from the Iowa High Technology Council     

Plasmid content in Yersinia pestis strains of different origin

Plasmid content in 242 Yersinia pestis strains from various natural plague foci of the U.S.S.R. and other countries was studied. Of these strains, 172 (71%) were shown to carry three plasmids described previously of about 6, 45-50 and 60 MDa, respectively. Twenty strains (8%) from different foci harboured additional cryptic plasmids, most often of about 20 mDa in size. Plasmid pPst displayed considerable constancy of its molecular mass. On the contrary, size variations of pCad (45-49 MDa) and, especially, pFra (60-190 MDa) were found. Molecular mass of these plasmids correlated with the host strain origin.     

Structural and regulatory genes for coli surface associated antigen 4 (CS4) are encoded by separate plasmids in enterotoxigenic Escherichia coli strains of serotype 025.H42

Two enterotoxigenic Escherichia coli strains of serotype 0.25.H42 that produced coli surface associated antigens CS4 and CS6 hybridized with a probe containing the cfaD sequence that regulates expression of colonization factor antigen CFA/I. Transformation of a cloned cfaD gene into some derivatives of the strains that were negative for CS4 and CS6 resulted in expression of CS4 but not CS6. By hybridization the sequence that regulated CS4 production in the wild type 025 strains was located on a plasmid that also encoded the CS6 antigen. The structural genes for the CS4 antigen were on a separate plasmid. The 025 strains carried a third plasmid encoding enterotoxin production which was therefore unlinked to regulation sequences or genes encoding CS antigens.