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Journal of Virology, February 2001, p. 1601-1610, Vol. 75, No. 4
0022-538X/01/$04.00+0   DOI: 10.1128/JVI.75.4.1601-1610.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

ATP-Dependent Simian Virus 40 T-Antigen-Hsc70 Complex Formation

Christopher S. Sullivan, Susan P. Gilbert, and James M. Pipas*

Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260

Received 20 September 2000/Accepted 6 November 2000

Simian virus 40 large T antigen is a multifunctional oncoprotein that is required for numerous viral functions and the induction of cellular transformation. T antigen contains a J domain that is required for many of its activities including viral DNA replication, transformation, and virion assembly. J-domain-containing proteins interact with Hsc70 (a cellular chaperone) to perform multiple biological activities, usually involving a change in the conformation of target substrates. It is thought that Hsc70 associates with T antigen to assist in performing its numerous activities. However, it is not clear if T antigen binds to Hsc70 directly or induces the binding of Hsc70 to other T-antigen binding proteins such as pRb or p53. In this report, we show that T antigen binds Hsc70 directly with a stoichiometry of 1:1 (dissociation constant = 310 nM Hsc70). Furthermore, the T-antigen-Hsc70 complex formation is dependent upon ATP hydrolysis at the active site of Hsc70 (ATP dissociation constant = 0.16 µM), but T-antigen-Hsc70 complex formation does not require nucleotide hydrolysis at the T-antigen ATP binding site. N136, a J domain-containing fragment of T antigen, does not stably associate with Hsc70 but can form a transient complex as assayed by centrifugation analysis. Finally, T antigen does not associate stably with either of two yeast Hsc70 homologues or an amino-terminal fragment of Hsc70 containing the ATPase domain. These results provide direct evidence that the T-antigen-Hsc70 interaction is specific and that this association requires multiple domains of both T antigen and Hsc70. This is the first demonstration of a nucleotide requirement for the association of T antigen and Hsc70 and lays the foundation for future reconstitution studies of chaperone-dependent tumorigenesis induced by T antigen.

* Corresponding author. Mailing address: Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260. Phone: (412) 624-4691. Fax: (412) 624-9311. E-mail: pipas+{at}pitt.edu.

Journal of Virology, February 2001, p. 1601-1610, Vol. 75, No. 4
0022-538X/01/$04.00+0   DOI: 10.1128/JVI.75.4.1601-1610.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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Copyright © 2001 by the American Society for Microbiology. All rights reserved.