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J. Bacteriol., 08 1996, 4975-4983, Vol 178, No. 16
MW Climo, VK Sharma and GL Archer
The genes mediating the conjugative transfer of the 52-kb staphylococcal
plasmid pGO1 are within a 14.4-kb gene cluster designated trs. However, a
clone containing trs alone cannot transfer independently and no candidate
oriT has been found within or contiguous to trs. In this study, we
identified a 1,987-bp open reading frame (ORF) 24 kb 3' and 13 kb 5' to trs
that was essential for conjugative transfer: transposon insertions into the
ORF abolished transfer and a plasmid containing the ORF could complement
these transposon- inactivated pGO1 mutants for transfer. Analysis of the
nucleotide sequence of this ORF revealed significant homology between the
amino terminus of its predicted protein and those of several
single-stranded endonucleases. In addition, a 12-bp DNA sequence located
100 bp 5' to the ORF's translational start site was identical to the oriT
sequences of the conjugative or mobilizable plasmids RSF1010, pTF1, R1162,
pSC101, and pIP501. The ability of the ORF, designated nes (for nicking
enzyme of staphylococci), to generate a single-stranded nick at the oriT
was demonstrated in Escherichia coli by alkaline gel and DNA sequence
analysis of open circular plasmid DNA. Plasmids that could be converted to
the open circular form by the presence of oriT and nes could also be
mobilized at high frequency into Staphylococcus aureus recipients with a
second plasmid containing only trs. We propose that the 14.4 kb of trs and
the approximately 2.2 kb of the oriT-nes region, coupled with an origin of
replication, make up the minimal staphylococcal conjugative replicon.
Copyright © 1996, American Society for Microbiology
Identification and characterization of the origin of conjugative transfer (oriT) and a gene (nes) encoding a single-stranded endonuclease on the staphylococcal plasmid pGO1
Department of Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298-0049, USA.
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