PubMed Health⌕ Search

Biomedical subjects

B E Uhlin

Publications and source records attributed to B E Uhlin.

58 records · Page 4Linked to original sources
PubMed1975

Plasmid incompatibility and control of replication: copy mutants of the R-factor R1 in Escherichia coli K-12.

Plasmid incompatibility was studied in Escherichia coli K-12. By double-antibiotic selection, clones were constructed that carried the two R-factors R1 and R100, both belonging to the compatibility group FII. After release of the selection pressure, each of the two plasmids was lost at the same rate (8% per generation). Mutants of R-factor R1 showing an increased number of copies per chromosome (copy mutants) were tested for their incompatibility towards R-factor R100. The results indicate that plasmid incompatibility is quantitative and not just a qualitative property. All copy mutants studied affected incompatibility, and there were two classes of mutants: one increasing and one decreasing the incompatiblity exerted towards the test plasmid R100. Evidence is presented that incompatibility is related to the mechanisms that control replication. The implications of such a relation on proposed models for control of replication are discussed. The data do not support the hypothesis that plasmid incompatibility is due to competition for a replicational or segregational site.

Ampicillin↗
PubMedDate not supplied

New runaway-replication-plasmid cloning vectors and suppression of runaway replication by novobiocin.

Two new cloning vectors (pBEU28 and pBEU50) with temperature-controlled runaway-replication properties are described. pBEU28 is similar to aphA+ (KanR) plasmid pBEU2 but lacks a 1.8-kb duplication which is responsible for plasmid instability. pBEU50 is an analog of pBR313 and pBR322 in that it carries bla+(AmpR), which can be used for selection, and tet+(TetR) which can be inactivated by cloning at HindIII and BamHI restriction sites. Sublethal concentrations of novobiocin were exploited to suppress runaway replication and to restore the viability of the plasmid carriers. By this method copB deletion mutants of two temperature-controlled, conditional runaway-replication plasmids were detected and isolated. The unconditional runaway-replication property of these plasmids leads us to hypothesize that there are at least two controls of plasmid R1 copy number and that the copB-dependent control is temperature-sensitive in the conditional runaway replication mutants. The novobiocin suppression of the runaway replication permitted us to clone dnaN+ on pBEU28 and to identify its presence at 42 degrees C with a dnaN59 transformation recipient which was temperature-sensitive due to a defect in the dnaN gene.

Base Sequence↗