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  • 1
    ISSN: 1617-4623
    Keywords: ColE1 ; Plasmid mobilization ; Overlapping genes ; Site-directed mutagenesis ; Relaxation complex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A third of the 6.6 kb genome of ColE1 is devoted to mobilization (mob) genes necessary to promote its specific transfer in the presence of conjugative plasmids. Themob region is genetically complex: twomob genes are entirely overlapped by a third. Oligonucleotide-directed mutagenesis was used to insert an amber codon into one of the overlapped genes and make possible a full complementation analysis ofmob. Fourmob genes essential for mobilization by R64drd11 were thus identified. Fragments ofmob were subcloned under control of the Ptac promoter in a suitable vector, overexpressed in minicells and the mobilization proteins visualized. A comprehensive alignment of themob region of ColE1 with those of its close relatives ColK and ColA demonstrating that the four essentialmob genes are conserved is also presented.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1617-4623
    Keywords: ColE1 ; Mobilization ; Transfer origin ; Lambda plasmid vectors ; Integration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mobilization of the plasmid ColE1 from cells containing a conjugative plasmid (such as F) requires the synthesis of ColE1 mob proteins, and the presence, in cis, of bom (basis of mobility), a region of ColE1 containing the origin of transfer (oriT). The process of ColE1 transfer is thought to resemble that of the conjugative plasmid F, although the plasmids share little sequence homology. In F, conjugation is preceded by a strand-specific nicking event at oriT. The nicked strand is then conducted to the recipient with the 5′ end leading. This is believed also to occur with ColE1, but direct biochemical confirmation has been precluded by its small size (6.65 kb). To test this hypothesis genetically, a novel method, using a λdv-based vector, has been devised to site-specifically integrate bom (or any other cloned sequence) into the chromosome of Escherichia coli. When provided with suitable mobilizing plasmids, such strains were found to transfer the chromosome in a polar way. From these data, the orientation of transfer of ColE1 was deduced and shown to be analogous to F.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    BioEssays 2 (1985), S. 209-211 
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Bacterial plasmids are ubiquitous ‘minichromosomes’ that have major importance in clinical microbiology, as agents of pathogenicity and as carriers of antibiotic resistance, and in molecular genetics, through their role as vectors in gene manipulation. Plasmids carry a wide range of dispensable, transiently useful and often bizarre functions.1 Naturally occurring plasmids, in addition to modifying the host cell phenotype, carry genes involved in the control of their own vegetative replication, plasmid copy number2 and stable inheritance. They may also carry determinants for the conjugal transfer of DNA between bacteria.3 Whereas low-copy-number plasmids must be partitioned by some active process during cell division, the evidence suggests that multicopy plasmids are distributed randomly between daughter cells. Two independent determinants are necessary for the stable inheritance of multicopy plasmids, and both of these appear to act by maximizing the number of independent plasmid molecules.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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