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Journal of Bacteriology, July 2000, p. 4022-4027, Vol. 182, No. 14
Department of Biological Sciences, University
of Alberta, Edmonton, Alberta, Canada T6G 2E9
Received 20 October 1999/Accepted 17 April 2000
Cleavage at the F plasmid nic site within the origin of
transfer (oriT) requires the F-encoded proteins TraY and
TraI and the host-encoded protein integration host factor in vitro. We confirm that F TraY, but not F TraM, is required for cleavage at
nic in vivo. Chimeric plasmids were constructed which
contained either the entire F or R100-1 oriT regions or
various combinations of nic, TraY, and TraM binding sites,
in addition to the traM gene. The efficiency of cleavage at
nic and the frequency of mobilization were assayed in the
presence of F or R100-1 plasmids. The ability of these chimeric
plasmids to complement an F traM mutant or affect F
transfer via negative dominance was also measured using transfer efficiency assays. In cases where cleavage at nic was
detected, R100-1 TraI was not sensitive to the two-base difference in
sequence immediately downstream of nic, while F TraI was
specific for the F sequence. Plasmid transfer was detected only when
TraM was able to bind to its cognate sites within oriT.
High-affinity binding of TraY in cis to oriT
allowed detection of cleavage at nic but was not
required for efficient mobilization. Taken together, our results
suggest that stable relaxosomes, consisting of TraI, -M, and -Y
bound to oriT are preferentially targeted to the transfer apparatus (transferosome).
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Mobilization of Chimeric oriT Plasmids
by F and R100-1: Role of Relaxosome Formation in Defining Plasmid
Specificity
*
Corresponding author. Mailing address: Department of
Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9. Phone: (780) 492-0458. Fax: (780) 492-1903. E-mail:
laura.frost{at}ualberta.ca.
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