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Novel corynebacterial plasmids carrying alpha-amylase gene from Bacillus have been constructed. The level of alpha-amylase expression depends on the size of the vector. The highest expression levels were measured in brevibacteria harboring pA61 plasmid.
The plasmid DNA pMI10 (5310 bp) was isolated from the alpha-amylase producing strain B. subtilis A18. Thirteen restriction endonucleases were used to digest pMI10 DNA and the restriction map of pMI10 DNA was constructed by mapping PstI (1), HindII (2), BglI (2), BspRI (3) and HindIII (3) sites.
While studying antibiotic-resistant plasmids from multi-drug-resistant nosocomial Staphylococcus aureus strains, we isolated a small (2.889 kb) chloramphenicol-resistant (Cm(r)) plasmid, which was designated as pMC524/MBM. The molecular size of pMC524/MBM was close to that of pC194 (2.910 kb), a well-known Cm(r) staphylococcal plasmid. Unlike pC194, this plasmid can replicate and express itself efficiently and stably in Escherichia coli. However, Cm is needed for stable maintenance of pMC524/MBM in different hosts. In this study, the nucleotide sequences of these two plasmids were compared after sequencing of pMC524/MBM [EMBL Accession No. AJ312056 SAU312056]. Although these two plasmids have striking nucleotide sequence homology, the Plus Origin, Minus Origin, the replication protein (Rep), and the chloramphenicol acetyl transferase (Cat) have considerable variations. Possibly, these changes have modulated pMC524/MBM into an efficient shuttle-plasmid.
A cryptic plasmid designated pSBO2 (3582 bp) was isolated from Streptococcus bovis JB1. The pSBO2 contained putative sites for a double-strand origin (dso), a small transcriptional repressor protein (Cop), countertranscribed RNAs (ctRNAs), and a replication protein (Rep), which were similar to those from pMV158 and pLS1, which were isolated from S. agalactiae, and pWVO1, isolated from Lactococcus lactis. The putative single-strand origin (sso) of pSBO2 was similar to pER341 and pST1, which were isolated from S. thermophilus. Recombinant plasmid designated pSBE2 was constructed to bind pECM184 vector and the DNA fragment containing sso, dso, Cop, ctRNAs, and Rep of pSBO2. When pSBE2 was introduced into S. bovis 12-U-1 and no8, the plasmids in the transformants had deleted the 160-bp fragment between sso and dso. This plasmid, designated pSBE2A, was capable of transforming Escherichia coli and S. bovis strains 12-U-1 and no8 on high frequency; therefore, pSBE2A is an effective shuttle vector.
The complete sequence of the leucine plasmid of Buchnera aphidicola from the aphid Acyrthosiphon pisum (pLeu-BAp) is reported. Its gene organization was concordant with those of other leucine plasmids of Buchnera from aphids of the Aphidini and Macrosiphini tribes. Three inverted repeats are present in pLeu-BAp. Two of them are also present in pLeu from the family Aphididae: (i) SIR1, located downstream the leucine operon, resembles a rho-independent terminator of transcription, and (ii) LIR1, located upstream of the leucine operon, is suggested to be involved in transcription termination or messenger stability. The third, located near the putative ATGC repeats involved in the origin of replication, is specific in aphids of the Macrosiphini tribe. Phylogenetic analyses based on sequences of leuA, leuB, leuC, leuD, repA1 and ORF1 showed a closer relationship between Buchnera (A. pisum) and Buchnera (Diuraphis noxia). However, tree topologies indicate that the split between both aphid species took place soon after the formation of the Macrosiphini lineage.
Plasmid-encoded aminoglycoside-(3)-N-acetyltransferase IV, AAC(3)-IV, was purified to homogeneity by affinity chromatography from E. coli. The enzyme was shown to consist of a monomer, with the apparent Mr being in agreement with that calculated from the nucleotide sequence of the aacC4 gene (Mr 28 500). Determination of the sequence of the N-terminal 6 amino acids revealed that processing did not occur, indicating the cytoplasmic localization of the AAC(3)-IV enzyme. A correlation of antibiotic resistance with Km values of the purified enzyme for a corresponding set of aminoglycoside substrates is discussed with respect to the mechanism of resistance in vivo.
The product of the F plasmid transfer gene, traN, is thought to be required for the formation of stable mating aggregates during F-directed conjugation. By testing chimeric plasmids that express F transfer region segments for complementation of F lac traN mutant transfer, we mapped traN to the F transfer region between trbC and traF. Both protein and DNA sequence analysis determined the traN product to be a large, 66,000-Mr, polypeptide that undergoes signal sequence processing. The mature polypeptide was associated with outer membrane protein fractions, and a protease accessivity test confirmed that at least one portion of TraN is exposed on the cell surface. Our DNA sequence analysis also revealed that another gene, trbE, is located between traN and traF. The product of trbE was identified and shown to be a small, integral, inner membrane protein. The mating efficiency and pilus-specific phage susceptibility of a trbE::kan insertion mutant suggested that trbE is not essential for F transfer from Escherichia coli K-12 under standard mating conditions.
We have identified a plasmid DNA that is found within mitochondria of wild-type N. crassa strain Mauriceville-1c (FGSC #2225), but that shows no detectable sequence homology with mitochondrial DNA. The plasmid DNA consists of an oligomeric series of circular molecules of monomer length 3.6 kb. There are two unusual clusters of restriction enzyme sites, one consisting of six Eco RI sites in a 1 kb region, and the other of five or more Pst I sites in a 0.4 kb region. RNA gel transfer hybridization experiments show a major transcript 3.3 to 3.4 kb long, close to the monomer length of the plasmid. The latter finding implies that the plasmid DNA contains specific sites for the initiation and termination of transcription.
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Haemophilus influenzae plasmid pVe445 (4.6 MDa) has been compared with Neisseria gonorrhoeae plasmids pNG18 (3.3 MDa) and pNG10 (4.6 MDa) by heteroduplex and restriction enzyme analysis. This study demonstrates that pVe445 differs from pNG18 only that it carries an additional 1.3-MDa DNA fragment between coordinates 0.9 and 2.2. Heteroduplex studies demonstrated that pNG10 and pVe445 are indistinguishable whereas restriction endonuclease analysis indicated minor differences in the distribution of AluI sites.
A restriction map of the 30-kb nonconjugative Pseudomonas plasmid pVS1 was constructed. Derivatives of pVS1 obtained in vitro by successive deletions were used to localize on the physical map the determinant for resistance to mercuric ions (carried by transposon Tn501), the gene(s) encoding sulfonamide resistance, a 1.6-kb region affecting plasmid stability and establishment in P. fluorescens ATCC 13525, and a segment required for mobilization of pVS1 by plasmid RP1. The sulfonamide resistance determinant of pVS1 appeared to be closely related to that of transposon Tn21. A mini-pVS1 replicon, pME259, consisting of an essential 1.55-kb segment (designated rep and thought to carry the origin of replication) and a mercury resistance determinant was able to replicate P. aeruginosa PAO but selective pressure was needed for plasmid maintenance. The copy number of pVS1 derivatives was estimated to be 6-8 per chromosome equivalent. Plasmids possessing the essential rep segment plus the adjacent stability region could be established in strains of P. aeruginosa, P. putida, P. fluorescens, P. acidovorans, P. cepacia, P. mendocina, P. stutzeri, P. syringae, Agrobacterium tumefaciens, and Rhizobium leguminosarum.
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.
All 201 multidrug resistant Salmonella typhimurium strains isolated from epidemics in India contained nonconjugative (157 strains) or conjugative (44 strains) Inc F1me multiresistance plasmids. Two small R-plasmids of 7 MDa which coded for resistance to either ampicillin or streptomycin and sulfamethoxazole were also detected along with other plasmids. The small plasmids were members of group 1 and group 2 incompatibility groups. Restriction endonuclease analysis of conjugative (96 MDa) and nonconjugative (88 MDa) Inc F1me plasmids showed considerable similarity except for the presence of unique fragments among both the groups and the loss of fragments corresponding to the smaller size of the nonconjugative plasmid. A single Inc F1me plasmid appears responsible for various outbreaks of multiresistant S. typhimurium in different parts of India.
Two 7.4-kb plasmids from Chlamydia psittaci have been cloned and characterized. These plasmids are quite distinct from the 6.2-kb C. psittaci and the C. trachomatis plasmids when compared by restriction endonuclease analysis. The plasmids show considerable cross-hybridization, with only a small region highly conserved and identified as a 4 X 22-bp tandemly repeated region. This sequence is identical in the two size categories of C. psittaci plasmids and differs from C. trachomatis plasmids by only 2 bp in the 22-bp motif. AT-rich clusters 5' to the repeat region which are present in C. trachomatis and Escherichia coli plasmids were absent from both classes of C. psittaci plasmids. Extensive regions are less highly conserved but show a sufficient degree of cross-hybridization to suggest that the plasmids are homologous.
Three cryptic DNA plasmids have been identified in a strain of the yeast Pichia inositovora that are 18, 13, and 10 kbp in size. All are sensitive to digestion by DNase I, restriction endonucleases, and exonuclease III, but are resistant to the activities of RNase A and lambda exonuclease. These results indicate that each plasmid is a linear DNA molecule whose 5' ends are protected. A restriction map has been developed for each of the plasmids, demonstrating that each is unique and confirming their linear nature. The plasmids are a major constituent of DNA prepared from whole cells, but are absent from DNA preparations of purified mitochondria and nuclei, indicating that the plasmids are located in the cytoplasm. These plasmids share many of the physical characteristics described for the linear plasmids of the yeasts Kluyveromyces lactis and Saccharomycopsis crataegensis. Unlike the linear plasmids of K. lactis, however, they appear not to be capable of killer toxin production.
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