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J. Bacteriol., 09 1995, 4890-4899, Vol 177, No. 17
AN Binns, CE Beaupre and EM Dale
The transfer of DNA from Agrobacterium tumefaciens into a plant cell
requires the activities of several virulence (vir) genes that reside on the
tumor-inducing (Ti) plasmid. The putative transferred intermediate is a
single-stranded DNA (T strand), covalently attached to the VirD2 protein
and coated with the single-stranded DNA-binding protein, VirE2. The
movement of this intermediate out of Agrobacterium cells and into plant
cells requires the expression of the virB operon, which encodes 11 proteins
that localize to the membrane system. Our earlier studies showed that the
IncQ broad-host-range plasmid RSF1010, which can be transferred from
Agrobacterium cells to plant cells, inhibits the transfer of T-DNA from
pTiA6 in a fashion that is reversed by overexpression of virB9, virB10, and
virB11. Here, we examined the specificity of this inhibition by following
the transfer of other T-DNA molecules. By using extracellular
complementation assays, the effects of RSF1010 on movement of either VirE2
or an uncoated T strand from A. tumefaciens were also monitored. The
RSF1010 derivative plasmid pJW323 drastically inhibited the capacity of
strains to serve as VirE2 donors but only partially inhibited T-strand
transfer from virE2 mutants. Further, we show that all the virB genes
tested are required for the movement of VirE2 and the uncoated T strand as
assayed by extracellular complementation. Our results are consistent with a
model in which the RSF1010 plasmid, or intermediates from it, compete with
the T strand and VirE2 for a common transport site.
Copyright © 1995, American Society for Microbiology
Inhibition of VirB-mediated transfer of diverse substrates from Agrobacterium tumefaciens by the IncQ plasmid RSF1010
Department of Biology, University of Pennsylvania, Philadelphia 19104- 6018, USA.
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