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Molecular and Cellular Biology, December 1998, p. 7466-7477, Vol. 18, No. 12
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
The 2µm Plasmid Stability System: Analyses of the
Interactions among Plasmid- and Host-Encoded Components
Soundarapandian
Velmurugan,
Yong-Tae
Ahn,
Xian-Mei
Yang,
Xu-Li
Wu, and
Makkuni
Jayaram*
Department of Microbiology and Institute of
Cell and Molecular Biology, University of Texas at Austin, Austin,
Texas 78712
Received 9 June 1998/Returned for modification 27 July
1998/Accepted 24 August 1998
The stable inheritance of the 2µm plasmid in a growing population
of Saccharomyces cerevisiae is dependent on two
plasmid-encoded proteins (Rep1p and Rep2p), together with the
cis-acting locus REP3 (STB). In
this study we demonstrate that short carboxy-terminal deletions of
Rep1p and Rep2p severely diminish their normal capacity to
localize to the yeast nucleus. The nuclear targeting, as well as their
functional role in plasmid partitioning, can be restored by the
addition of a nuclear localization sequence to the amino or the carboxy
terminus of the shortened Rep proteins. Analyses of deletion
derivatives of the Rep proteins by using the in vivo dihybrid genetic
test in yeast, as well as by glutathione S-transferase fusion trapping assays in vitro demonstrate that the amino-terminal portion of Rep1p (ca. 150 amino acids long) is responsible for its
interactions with Rep2p. In a monohybrid in vivo assay, we have
identified Rep1p, Rep2p, and a host-encoded protein, Shf1p, as being
capable of interacting with the STB locus. The Shf1 protein expressed in Escherichia coli can bind with high
specificity to the STB sequence in vitro. In a yeast strain
deleted for the SHF1 locus, a 2µm circle-derived plasmid
shows relatively poor stability.
*
Corresponding author. Mailing address: Department of
Microbiology, University of Texas at Austin, Austin, TX 78712. Phone: (512) 471-0966. Fax: (512) 471-5546. E-mail:
jayaram{at}almach.cc.utexas.edu.
Molecular and Cellular Biology, December 1998, p. 7466-7477, Vol. 18, No. 12
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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