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Journal of Virology, January 1999, p. 214-224, Vol. 73, No. 1
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Transactivation of a Ribosomal Gene by Simian Virus 40 Large-T Antigen Requires at Least Three Activities of the Protein

Jane F. Cavender,1,* Christine Mummert,2 and Mary Judith Tevethia2

Department of Biology, Elizabethtown College, Elizabethtown, Pennsylvania 17022,1 and Department of Microbiology and Immunology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 170332

Received 30 January 1998/Accepted 18 September 1998

Simian virus 40 large-T antigen transactivates the ribosomal genes which are transcribed by RNA polymerase (pol I), as well as genes that are dependent on either pol II or pol III. This report identifies regions and activities of T antigen that are required to transactivate a pol I-dependent rat ribosomal gene promoter. By using the rat ribosomal gene (rDNA) promoter linked to a chloramphenicol acetyltransferase gene, we show that at least three separable T-antigen regions are necessary to achieve wild-type levels of transactivation of rDNA in transiently transfected monkey cells. One activity depends on the region of T antigen shared with small-t antigen (T/t common region). A second activity maps to amino acids 109 to 626 and is highly sensitive to mutational inactivation. Complementation analyses suggest that at least one activity in this region is independent of and must be in cis with the activity within the T/t common region. In addition, a functional nuclear localization signal is required for maximal T-antigen-mediated transactivation of rat rDNA. The three activities work in concert to override cellular species-specific controls and transactivate the rat ribosomal gene promoter. Finally, we provide evidence that although the tumor suppressor protein Rb has been shown to repress a pol I-dependent promoter, transactivation of the rat rDNA promoter does not depend on T antigen's ability to bind the tumor suppressor product Rb.

* Corresponding author. Mailing address: Department of Biology, Elizabethtown College, One Alpha Dr., PA 17022-2298. Phone: (717) 361-1448. Fax: (717) 361-1176. E-mail: cavender{at}acad.etown.edu.

Journal of Virology, January 1999, p. 214-224, Vol. 73, No. 1
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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