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Mol Cell Biol, May 1998, p. 2677-2687, Vol. 18, No. 5
Department of Biochemistry, Tufts University
School of Medicine, Boston, Massachusetts 02111
Received 17 November 1997/Returned for modification 2 January
1998/Accepted 3 February 1998
Initiation of simian virus 40 (SV40) DNA replication is dependent
upon the assembly of two T-antigen (T-ag) hexamers on the SV40 core
origin. To further define the oligomerization mechanism, the
pentanucleotide requirements for T-ag assembly were investigated. Here,
we demonstrate that individual pentanucleotides support hexamer
formation, while particular pairs of pentanucleotides suffice for the
assembly of T-ag double hexamers. Related studies demonstrate that T-ag
double hexamers formed on "active pairs" of pentanucleotides
catalyze a set of previously described structural distortions within
the core origin. For the four-pentanucleotide-containing wild-type SV40
core origin, footprinting experiments indicate that T-ag double
hexamers prefer to bind to pentanucleotides 1 and 3. Collectively,
these experiments demonstrate that only two of the four
pentanucleotides in the core origin are necessary for T-ag assembly and
the induction of structural changes in the core origin. Since all four
pentanucleotides in the wild-type origin are necessary for extensive
DNA unwinding, we concluded that the second pair of pentanucleotides is
required at a step subsequent to the initial assembly process.
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Assembly of T-Antigen Double Hexamers on the Simian
Virus 40 Core Origin Requires Only a Subset of the Available
Binding Sites

*
Corresponding author. Mailing address: Department of
Biochemistry A703, Tufts University School of Medicine, 136 Harrison Ave., Boston, MA 02111. Phone: (617) 636-0447. Fax: (617) 636-6409. E-mail: PBULLOCK{at}OPAL.TUFTS.EDU.
Present address: Graduate Program in Molecular Biology,
Sloan-Kettering Cancer Center, New York, NY 10021.
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