Formation of a recombinant plasmid designated pNH603 was observed when two plasmids from incompatibility group X, the multicopy plasmid pNH602 (a higher-copy-number deletion derivative of R6K) and the oligocopy plasmid R485, coexisted in a single Escherichia coli cell. According to its size and its restriction endonuclease cleavage pattern, plasmid pNH603 is a true cointegrate of pNH602 and R485. An insertion-sequence-like element coming from plasmid R485 is supposed to mediate the fusion of both replicons. The pNH603 copy number (1-2 per chromosome) indicates that the mechanism of replication of the low-copy-number plasmid is dominant in this cointegrate. No dissociation of pNH603 to parental plasmids was observed even in E. coli K-12 recA+ cells. On the other hand, deletion derivatives of four size classes originate from pNH603 in both recA+ and recA hosts. A miniplasmid designated pNH604, a representative of the most frequent 7 Mg/mol size class, was found, in a low number of copies per host chromosome.

• MeSH
• deoxyribonukleasa BamHI MeSH
• deoxyribonukleasa EcoRI MeSH
• DNA bakterií analýza   izolace a purifikace   ultrastruktura   MeSH
• elektroforéza v polyakrylamidovém gelu MeSH
• elektronová mikroskopie MeSH
• Escherichia coli genetika   MeSH
• plazmidy * MeSH
• rekombinace genetická MeSH
• replikace DNA MeSH
• restrikční enzymy MeSH
• transpozibilní elementy DNA MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• deoxyribonukleasa BamHI MeSH
• deoxyribonukleasa EcoRI MeSH
• DNA bakterií MeSH
• restrikční enzymy MeSH
• transpozibilní elementy DNA MeSH

A stable deletion derivative pNH602 was obtained when the recently described higher-copy-number point mutant pNH601 of plasmid R6K was introduced to a minicells-producing strain of Escherichia coli. The size of plasmid pNH602 is 18.8 Mg/mol as determined by electron microscopy. The 7.2 Mg/mol fragment of R6K genome missing in pNH602 carries the Smr-determinant and the region finO and, according to the results of restriction analysis, it includes one EcoRI site. With its radioisotopically determined 33 copies of pNH602 per E. coli K-12 chromosome (npc), representing a 23% increase of the point mutant pNH601 and 150% enhancement of R6K npc, plasmid pNH602 differs from another closely related R6K deletion derivative pAS3 of the same size which exhibits only 20 npc. Both pNH602 and pAS3 plasmids are conjugative.

• MeSH
• chromozomální delece * MeSH
• DNA bakterií izolace a purifikace   MeSH
• druhová specificita MeSH
• elektronová mikroskopie MeSH
• Escherichia coli genetika   MeSH
• genotyp MeSH
• konjugace genetická MeSH
• mutace * MeSH
• plazmidy * MeSH
• restrikční enzymy MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• DNA bakterií MeSH
• restrikční enzymy MeSH

A stable copy-number mutant (pNH601) of plasmid R6K was isolated by selection for increased resistance to ampicillin determined by this plasmid. The size of the mutant plasmid was found to be unchanged (26 Mg/mol) but it is present in 27 copies of pNH601 per E. coli K-12 chromosome which represents a two-fold increase of R6K copy number value. The following genetic properties of pNH601 are reported and compared with those of R6K: conjugative transfer, fertility inhibition of plasmids belonging to other incompatibility groups, incompatibility with plasmid R485 under both non-selective and selective conditions and the integrative suppression of the dnaA ts mutation. The mutant plasmid pNH601 was found to be different from the original R6K in most of these properties.

• MeSH
• ampicilin farmakologie   MeSH
• DNA bakterií analýza   MeSH
• Escherichia coli analýza   účinky léků   genetika   MeSH
• konjugace genetická MeSH
• kruhová DNA analýza   MeSH
• mutace * MeSH
• R-plasmidy * MeSH
• streptomycin farmakologie   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• ampicilin MeSH
• DNA bakterií MeSH
• kruhová DNA MeSH
• streptomycin MeSH