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Journal of Bacteriology, November 1998, p. 5660-5667, Vol. 180, No. 21
Section of Microbiology, Cornell University,
Ithaca, New York 14853
Received 4 June 1998/Accepted 25 August 1998
The vir regions of octopine-type and nopaline-type Ti
plasmids direct the transfer of oncogenic T-DNA from
Agrobacterium tumefaciens to the nuclei of host plant
cells. Previous studies indicate that at least two genetic loci at the
left ends of these two vir regions are sufficiently
conserved to form heteroduplexes visible in the electron
microscope. To initiate an investigation of these genetic loci, we
determined the DNA sequences of these regions of both Ti plasmids and
identified both conserved loci. One of these is the 2.5-kb
virH locus, which was previously identified on the octopine-type Ti plasmid but thought to be absent from the
nopaline-type Ti plasmid. The virH operon contains two
genes that resemble P-450-type monooxygenases. The other locus encodes
a 0.5-kb gene designated virK. In addition, we identified
other potential genes in this region that are not conserved
between these two plasmids. To determine (i) whether these genes are
members of the vir regulon and, (ii) whether they are
required for tumorigenesis, we used a genetic technique to disrupt each
gene and simultaneously fuse its promoter to lacZ.
Expression of these genes was also measured by nuclease S1 protection
assays. virK and two nonconserved genes, designated virL and virM, were strongly induced by the
vir gene inducer acetosyringone. Disruptions of
virH, virK, virL, or
virM did not affect tumorigenesis of
Kalanchöe diagramontiana leaves or carrot
disks, suggesting that they may play an entirely different role during
pathogenesis.
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Wound-Released Chemical Signals May Elicit Multiple Responses
from an Agrobacterium tumefaciens Strain Containing an
Octopine-Type Ti Plasmid
*
Corresponding author. Mailing address: Section of
Microbiology, Wong Hall, Cornell University, Ithaca, NY 14853. Phone:
(607) 255-2413. Fax: (607) 255-3904. E-mail:
scw2{at}cornell.edu.
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