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1.
K Shimada T Nakamura S Maeda Y Takagi 《Biochemical and biophysical research communications》1977,75(3):659-666
Ampicillin-resistant colonies that did not utilize galactose appeared sporadically in cultures of galactose genedeleted K-12 cells containing colicin E1 factor carrying genes for galactose utilization and ampicillin resistance. Most of these colonies contained small plasmid DNAs. These plasmids existed as monomer DNAs within K-12 cells and formed a series of covalently closed circular DNA molecules ranging in size from 6.3 × 106 to 15.1 × 106 daltons. The use of these plasmid DNAs was discussed. 相似文献
2.
An electron microscope heteroduplex study of the ribosomal DNAs of Xenopus laevis and Xenopus mulleri 总被引:15,自引:0,他引:15
The arrangement of the genes and spacers has been analyzed in ribosomal DNA of Xenopus laevis and Xenopus mulleri by heteroduplex mapping and visualization of ribosomal RNA-DNA hybrids. Heterologous reassoeiated molecules show a characteristic pattern in which two perfectly duplexed regions, whose lengths are those predicted by the known lengths of the 18 S and 28 S genes, are separated by a small substitution loop of about 0.23 × 106 daltons and a large region of partial homology which averages 3.24 × 106 daltons. These mismatched regions are entirely consistent with the known sequence divergence previously described (Brown et al., 1972) for the transcribed and non-transcribed spacer regions of the two rDNAs, respectively. Hybrids of X. laevis rDNA with 18 S and 28 S rRNA contain two duplex regions of the expected lengths for the 18 S and 28 S genes separated by 0.49 × 106 daltons of single-strand DNA. This latter value is the length of the transcribed spacer region between the 18 S and 28 S RNAs that has been measured within the 40 S RNA precursor molecule by secondary structure mapping (Wellauer &; Dawid, personal communication). There is also a longer single-strand region separating one 18 S + 28 S gene set from the next; this is considered to be mainly non-transcribed spacer.We conclude that the 18 S and 28 S genes are separated by about 0.5 × 106 daltons of DNA of which about half is homologous in the two Xenopus species. This region is part of the transcribed spacer. In addition, the longer non-transcribed spacer can be seen to have some homology between the two species; the location of this homology is fairly reproducible between molecules and has been carefully documented by contour length measurements. 相似文献
3.
Homology of plasmids in strains of unicellular Cyanobacteria. 总被引:17,自引:0,他引:17
Six strains of unicellular cyanobacteria were examined for the presence of plasmids. Analysis of lysates of these strains by CsCl-ethidium bromide density centrifugation yielded a major chromosomal DNA band and a minor band containing covalently closed circular plasmid DNA, as shown by electron microscopy and agarose gel electrophoresis. The sizes of the various plasmid species were determined; in each of the Synechococcus strains 6301, 6707, and 6908 two plasmid species were found with molecular weights of 5.3 × 106 and 32.7 × 106. Synechococcus strain 7425 had two plasmids of molecular weight 5.4 × 106 and 24 × 106. Synechococcus strain 6312 and Synechocystis strain 7005 each contained one plasmid species with molecular weight of 15.9 × 106 and 2.0 × 106, respectively. Restriction enzyme analysis revealed identical cleavage patterns for the plasmids of identical molecular weight. 相似文献
4.
Summary Plasmids of three different sizes, designated as plasmid A (mw: 65×106), plasmid B (mw: 41×106) and plasmid C (mw: 32×106) respectively, have been isolated from various hemolytic wild-type strains ofE. coli. DNA-DNA hybridization was performed to determine their relationship.
The wild-type strain, PM167a, harbours plasmids of all three sizes. Hybridization studies indicate that all three plasmids
share extented sequence homologies but that plasmid A is not composed of plasmids B and C. Hybridization between plasmids
of the donor strain and those of appropriate transconjugants demonstrates that in some cases plasmids with identical size
are not longer completely homologous in their nucleotide sequences. This indicates that despite their defined sizes these
plasmids are not stable genetic entities, but rather they undergo frequently recombination and dissociation during conjugation.
In one particular transconjugant strain, K12-PM152/1, a plasmid D was found which is a stable recombined molecule of plasmids
B and C of the original strain.
Plasmids of size B found as the only extrachromosomal elements in a hemolytic wild-type strain (P224) and two transconjugant
strains (e.g. K12-CM20 and K12-PM167/1) share extended nucleotide sequence homologies but are not identical.
Little sequence homology was observed between two different hemolytic plasmids and the F and the Col Ib plasmids suggesting
that the former do not belong to either the F-like or the I-like group of plasmids. Another hemolytic plasmid is F-like based
on its sequence homologies with the F factor. 相似文献
5.
6.
A multiple plasmid-containing Escherichia coli strain: convenient source of size reference plasmid molecules. 总被引:154,自引:0,他引:154
A strain of Escherichia coli is described that contains eight plasmid species ranging in size from 1.36 × 106 to 35.8 × 106 daltons. This strain can be employed as a single source of covalently closed circular deoxyribonucleic acid molecules of different sizes for use as references in agarose gel electrophoretic analysis. 相似文献
7.
Molecular characterization of a stable Flac plasmid 总被引:2,自引:0,他引:2
F L Macrina E Balbinder A Bassel 《Biochemical and biophysical research communications》1973,54(2):737-743
FS is a thermostable extrachromosomal element isolated in which is altered in its replication as compared to its precursor Fts114. Sedimentation of both these plasmids in alkaline sucrose gradients has indicated a difference in their sizes. Contour length measurements of open circular plasmid DNA molecules photographed in the electron microscope have revealed the estimated molecular weight of Fts114 to be 81 × 106 daltons while that of FS is 109 × 106 daltons. FS may carry a segment of chromosomal or cryptic plasmid DNA. 相似文献
8.
DNA of ciliated protozoa: DNA sequence diminution during macronuclear development of oxytricha 总被引:1,自引:0,他引:1
We have measured the reassociation kinetics of DNA from the micronucleus and from the macronucleus of the hypotrichous cillate Oxytricha. The micronuclear DNA reassociates with at least a two-component reaction, indicating the presence of both repeated and non-repeated sequences. The kinetic complexity of micronuclear non-repeated DNA is in the range of 2 to 15 × 1011 daltons; the haploid DNA content of the micronucleus is 4 × 1011 daltons (0.66 pg), measured microspectrophotometrically. The DNA of the macronucleus reassociates as a single second-order reaction, with a kinetic complexity of 3.6 × 1010 daltons. A comparison of the kinetic complexities of micronuclear and macronuclear DNAs suggest a 5 to 30 fold reduction in DNA sequence complexity during the formation of a macronucleus from a micronucleus. Macronuclear DNA is in pleces with an average molecular weight of 2.1 × 106 daltons. Since the kinetic complexity of macronuclear DNA is 3.6 × 1010 daltons, the macronucleus must contain about 17,000 different kinds of DNA pieces.Each macronucleus contains 3.5 × 1013 daltons (58 pg) of DNA, indicating that each sequence must be present about 1000 times per macronucleus or 2000 times per cell. 相似文献
9.
The use of genetically engineered bacteria in natural environments constitutes a risk of transfer of recombinant DNA to the
indigenous bacteria. However, chromosomal genes are believed to be less likely to transfer than genes on mobilizable and conjugative
plasmids. To study this assumption, horizontal transfer of a recombinant gene cassette inserted into the chromosome of a Pseudomonas stutzeri strain, into a mobilizable plasmid (pAGM42), and into a conjugative plasmid (pKJK5) isolated from barley rhizosphere was
investigated. Horizontal transfer efficiencies of the gene cassette inserted into a conjugative plasmid was 8.20 × 10−3 transconjugants/(donors × recipients)1/2 in the rhizosphere and 4.57 × 10−2 transconjugants/(donors × recipients)1/2 in the spermosphere. Mobilization of the plasmid pAGM42 by the plasmids RP4 and pKJK5 was also detected at high levels in
the microcosms, transfer efficiencies were up to 4.36 × 10−3 transconjugants/(donors × recipients)1/2. Transfer of chromosomal encoded genes could not be detected in the microcosms by conjugation or transformation. However,
transformation did occur by using the same bacterial strains under laboratory conditions. The rhizosphere and especially the
spermosphere thus proved to be hot spot environments providing favorable conditions for gene transfer by mobilization and
conjugation, but these environments did not support transformation at a detectable level.
Received: 21 July 2000 / Accepted: 21 August 2000 相似文献
10.
K Matsubara 《Journal of molecular biology》1976,102(3):427-439
Strains of Saccharomyces cerevisiae carrying a small double-stranded RNA species (the killer plasmid) secrete a toxin which is lethal only to strains not carrying this plasmid.We have isolated mutants in eight chromosomal genes essential for replication or maintenance of the killer plasmid, called mak1 through mak8. Seven of these genes have been mapped. mak4 and mak5 are on chromosome II; mak1 and mak8 are on chromosome XV; mak3 and mak6 are on chromosome XVI; and mak7 is on chromosome VIII. We have not yet located mak2. Two other chromosomal genes, m and pets, have been shown to be required for replication or maintenance of the killer plasmid.One allele of mak1 results in temperature sensitivity for host growth. Two independent pets isolates also result in the petite phenotype, as well as temperature sensitivity for growth.Wild-type killer strains have been reported to carry two species of doublestranded RNA of 2.5 × 106 and 1.4 × 106 molecular weight (designated L and M, respectively); wild-type non-killers carried only L. We estimate the size of the L and M species at 3.0 × 106 and 1.7 × 106 daltons, respectively. We have also detected a third species of double-stranded RNA of molecular weight 3.8 × 106 (XL) present in all killer and non-killer strains examined.Mutation of any of mak1 through mak8 results in loss of the killer-associated species of double-stranded RNA (M; 1.7 × 106). These mutants retain both the L species (3.0 × 106) and the XL species (3.8 × 106) of double-stranded RNA, and have acquired two new minor RNA species. 相似文献
11.
Robert M. Faust John Spizizen Vivian Gage Russell S. Travers 《Journal of invertebrate pathology》1979,33(2):233-238
Four entomopathogenic bacteria contained extrachromosomal deoxyribonucleic acid (DNA) molecules of various sizes. Bacillus thuringiensis var. kurstaki contained twelve elements banding on agarose gels that ranged from 0.74 to > 50 × 106 daltons, three of which were giant extrachromosomal DNA elements. B. thuringiensis var. sotto contained one giant extrachromosomal DNA element with a molecular size of about 23.5 × 106 daltons and two lesser elements of 0.80 and 0.62 × 106 daltons. B. thuringiensis var. finitimus harbored two giant DNA elements corresponding to >50 × 106 daltons and two lesser bands with relative small size (0.98 and 0.97 × 106 daltons). B. popilliae contained no giant extrachromosomal DNA elements but did contain two smaller elements corresponding to 4.45 and 0.58 × 106 daltons. The possible use of extrachromosomal DNA elements that prove to be autonomous replicons for recombinant DNA studies is discussed. 相似文献
12.
Twelve strains ofLegionella pneumophila were tested for the presence of plasmid DNA. Three strains, belonging to serogroup 1, had large plasmids of 83.8×106 daltons, as determined by electron microscopy. A fourth strain, also from serogroup 1, had a similar large plasmid in addition to a smaller plasmid. Restriction analysis of plasmid DNA isolated from the strains with a single size plasmid indicated that the plasmids were structurally very similar. The biologic functions of these plasmids are yet to be determined. 相似文献
13.
Derivatives of a naturally occurring IncFII tetracycline resistance plasmid (pUB889) which are unable to confer resistance to tetracycline, and which were isolated from both partners of a married couple, have been examined. The tet genes are part of a transposon-like structure which is closely related to, but distinct from, Tn10. The lesions in the two plasmids examined are identical and involve the insertion of a nucleotide sequence of 0.9 × 106 within the region encoding tetracycline resistance, expression of which is lost as a consequence. The extra DNA is homologous with the nucleotide sequence, a pair of which form the inverted repeats of the Tn10-like structure. We conclude that this nucleotide sequence comprises an IS element. The epidemiological implications arising from the origin of these plasmids are discussed. 相似文献
14.
Conjugative R plasmids in Streptococcus agalactiae (group B). 总被引:24,自引:0,他引:24
Twenty-one drug-resistant clinical isolates of group B streptococci were investigated for drug-resistance transfer by conjugation. Six strains were resistant to tetracycline, two to chloramphenicol, one to both drugs, and twelve to macrolide antibiotics (erythromycin, oleandomycin and spiramycin), lincomycin, pristinamycin I, and/or chloramphenicol and tetracycline. Ten strains carried R plasmids which were transferable to group B and/or group D recipients by a conjugation-like phenomenon. Six plasmids were transferred at a high frequency (9 × 10?2 to 4 × 10?4) and four, at low frequency (5 × 10?6 to 7 × 10?8). The molecular weight of one plasmid (pIP501) was investigated after transfer into the new hosts and was found to be similar to that carried by the wild strain (19.8 × 106). 相似文献
15.
An expression plasmid was constructed, consisting of the promoter/operator region of the tryptophan operon from Serratia marcescens and a synthetic ribosome-binding site ligated into pBR322. Leukocyte-type interferon gene fragments (IFN-αA and IFN-αC) isolated from a cDNA library from human lymphoblastoid (Namalwa) cells were inserted into the unique HindIII site of the expression plasmid, and the resulting recombinant plasmids directed the synthesis of up to 5 × 105 units of A-type preinterferon, 2 × 107 units of A-type mature interferon and 8 × 105 units of C-type mature interferon per liter culture. 相似文献
16.
H. R. Smith G. O. Humphreys Geraldine A. Willshaw E. S. Anderson 《Molecular & general genetics : MGG》1976,143(3):319-325
Summary The properties of two plasmids coding for the EcoRI restriction and modification enzymes are described. Both plasmids are non auto-transferring (NTP) but can be mobilised by transfer factors. Strains carrying NTP13 produce colicin E1 and the EcoRI enzymes. This plasmid has a molecular weight of 6x106 daltons and is present as approximately 12 copies per chromosome. The second plasmid, NTP14, was detected after mobilisation of the EcoRI plasmid with the R factor R1–19. NTP14 codes for ampicillin resistance, synthesis of the EcoRI enzymes and colicin E1. The molecular weight of NTP14 is 10.7x106 daltons and there are about 14 copies per chromosome. DNA-DNA reassociation experiments were performed to determine the interrelationships of NTP13, NTP14, ColE1 and the R factor R1–19. NTP13 and NTP14 continue to replicate when cellular protein synthesis is inhibited by the addition of chloramphenicol. 相似文献
17.
Vilma A. Stanisich P. M. Bennett J. M. Ortiz 《Molecular & general genetics : MGG》1976,143(3):333-337
Summary The molecular properties of the P-group plasmids R26, R527 and R18-18 (a carbenicillin-sensitive derivative of R18) have been compared with those of RP1. R18-18 and RP1 have a MW about 38×106 daltons, and R26 and R527 of 52×106 daltons (determined from contour lengths). All three plasmids have a buoyant density similar to that of RP1 (1.719 g/cm3, 60% G+C). From their molecular and phenotypic similarities, these plasmids probably represent two pairs of identical or closely similar elements.Resistant bacteria are not recovered following F116L-mediated transduction of R26 (or R527), and this correlates with the plasmids' larger size (phage genome=40×106 daltons). Fragments of R26 are, however, transduced and their resistance determinants may be rescued by recombination if the recipient harbours R18-18. Such events are accompanied by an increase in the size of the recipient plasmid from 38×106 to 52×106 daltons following inheritance of the resistance determinants Sm Su Gm Hg, but not Cb. Thus, Sm Su Gm Hg are encoded in a DNA segment of MW about 14×106 daltons which apparently has no homologous region on R18-18. Since a piece of DNA of this MW also corresponds to the difference in size between R26 and R18-18, it is possible that the former is derived from an RP1-like element which has acquired these additional resistance determinants. 相似文献
18.
19.
DNA isolated from purified nuclei of Polytoma obtusum has a buoyant density of 1.711 g/ml in CsCl, a Tm of 91.3° C in SSC, and a G + C content of 52.5% as determined by base composition analysis. Thermal dissociation and reassociation studies indicated that this nuclear DNA contains a considerable amount of heterogeneity. Under appropriate reannealing conditions for denatured DNA, about 15% of the DNA reannealed to form a satellite peak at a density of 1.711 g/ml within one hour. Native DNA fractions of different average buoyant densities, ranging from 1.723 to 1.708 g/ml were also obtained in a preparative CsCl gradient, indicating the presence of intermolecular heterogeneity at a molecular size of 8.5×106 daltons. The nuclear DNA reassociated as three distinct classes. The very fast species constituted about 20 % of the total hyperchromicity, the class of intermediate rate comprised roughly 10% of the nuclear DNA, while the remaining 70% consisted of unique sequences. The haploid genome set was estimated by renaturation kinetics studies to contain 5.0×1010 daltons of DNA or 7.5×107 nucleotide pairs. The analytical complexity of the total nuclear genome was found to be 9.35×1010 daltons, thus indicating that vegetative cells of P. obtusum are diploid. 相似文献
20.
Geraldine A. Willshaw H. R. Smith E. S. Anderson 《Molecular & general genetics : MGG》1978,159(1):111-116
Summary The molecular sizes of F1
me resistance plasmids from strains of Salmonella typhimurium, S. wien and S. typhi were within the range 87.9–102.6×106 daltons. DNA reassociation studies indicated that the plasmids from these hosts had at least 80% of their nucleotide sequences in common. A high proportion of F1
me plasmids cannot mediate their own transfer. The non-autotransferring property of such plasmids is the result of DNA deletion; a non-autotransferring F1
me plasmid was about 10×106 daltons shorter than autotransferring representatives of the group, and its DNA showed 100% homology with them. Plasmids of the F1
me group are incompatible with the F factor and with F1R factors. F1
me plasmids are incompatible with the fi
+ MP10 plasmid of S. typhimurium, whereas F and F1 factors are compatible with MP10 (Anderson et al., 1977). There was no significant DNA homology between members of the F1
me group and MP10, and these plasmids may share only a small region of DNA responsible for their incompatibility. The F1
me R factors examined had 29–37% DNA homology with the F factor, and 50–58% homology with the F1 resistance plasmid, R162. Molecular examination therefore supports the genetic differentiation of members of the F1
me group from other F-like plasmids. Both types of investigation can thus be used in epidemiological studies of bacterial strains carrying resistance or other plasmids. 相似文献