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Journal of Bacteriology, April 2001, p. 2306-2315, Vol. 183, No. 7
Department of Biochemistry and Molecular
Biology, Faculty of Medicine, Dalhousie University, Halifax, Nova
Scotia, Canada B3H 4H7
Received 5 September 2000/Accepted 11 January 2001
Both of the Saccharomyces cerevisiae 2µm
circle-encoded Rep1 and Rep2 proteins are required for efficient
distribution of the plasmid to daughter cells during cellular division.
In this study two-hybrid and in vitro protein interaction assays
demonstrate that the first 129 amino acids of Rep1 are sufficient for
self-association and for interaction with Rep2. Deletion of the first
76 amino acids of Rep1 abolished the Rep1-Rep2 interaction but still
allowed some self-association, suggesting that different but
overlapping domains specify these interactions. Amino- or
carboxy-terminally truncated Rep1 fusion proteins were unable to
complement defective segregation of a 2µm-based stability vector with
rep1 deleted, supporting the idea of the requirement of Rep
protein interaction for plasmid segregation but indicating a separate
required function for the carboxy-terminal portion of Rep1. The results
of in vitro baiting assays suggest that Rep2 contains two
nonoverlapping domains, both of which are capable of mediating Rep2
self-association. The amino-terminal domain interacts with Rep1, while
the carboxy-terminal domain was shown by Southwestern analysis to have
DNA-binding activity. The overlapping Rep1 and Rep2 interaction domains
in Rep1, and the ability of Rep2 to interact with Rep1, Rep2, and DNA,
suggest a model in which the Rep proteins polymerize along the 2µm
circle plasmid stability locus, forming a structure that mediates
plasmid segregation. In this model, competition between Rep1 and Rep2
for association with Rep1 determines the formation or disassembly of
the segregation complex.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.7.2306-2315.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Functional Domains of Yeast Plasmid-Encoded
Rep Proteins

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Corresponding author. Mailing address: Department of
Biochemistry and Molecular Biology, Faculty of Medicine, Dalhousie
University, Halifax, Nova Scotia, Canada B3H 4H7. Phone: (902)
494-7182. Fax: (902) 494-1355. E-mail: DOBSON{at}is.dal.ca.
Present address: Department of Biotechnology, Royal Institute of
Technology, S-100 44 Stockholm, Sweden.
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