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Molecular and Cellular Biology, April 1999, p. 2455-2464, Vol. 19, No. 4
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

The J Domain of Papovaviral Large Tumor Antigen Is Required for Synergistic Interaction with the POU-Domain Protein Tst-1/Oct6/SCIP

Elisabeth Sock, Janna Enderich, and Michael Wegner*

Zentrum für Molekulare Neurobiologie, Universität Hamburg, D-20246 Hamburg, Germany

Received 10 August 1998/Returned for modification 14 October 1998/Accepted 4 January 1999

Large T antigens from polyomaviruses are multifunctional proteins with roles in transcriptional regulation, viral DNA replication, and cellular transformation. They have been shown to enhance the activity of various cellular transcription factors. In the case of the POU protein Tst-1/Oct6/SCIP, this enhancement involves a direct physical interaction between the POU domain of the transcription factor and the amino-terminal region of large T antigen. Here we have analyzed the structural requirements for synergistic interaction between the two proteins in greater detail. Tst-1/Oct6/SCIP and the related POU protein Brn-1 were both capable of direct physical interaction with large T antigen. Nevertheless, only Tst-1/Oct6/SCIP functioned synergistically with large T antigen. This differential behavior was due to differences in the amino-terminal regions of the proteins, as evident from chimeras between Tst-1/Oct6/SCIP and Brn-1. Synergy was specifically observed for constructs containing the amino-terminal region of Tst-1/Oct6/SCIP. Large T antigen, on the other hand, functioned synergistically with Tst-1/Oct6/SCIP only when the integrity of its J-domain-containing amino terminus was maintained. Mutations that disrupted the J domain concomitantly abolished the ability to enhance the function of Tst-1/Oct6/SCIP. The J domain of T antigen was also responsible for the physical interaction with Tst-1/Oct6/SCIP and could be replaced in this property by other J domains. Intriguingly, a heterologous J domain from a human DnaJ protein partially substituted for the amino terminus of T antigen even with regard to the synergistic enhancement of Tst-1/Oct6/SCIP function. Given the general role of J domains, we propose chaperone activity as the underlying mechanism for synergy between Tst-1/Oct6/SCIP and large T antigens.

* Corresponding author. Mailing address: ZMNH, Martinistr. 52, D-20246 Hamburg, Germany. Phone: 49 40 42803 6274. Fax: 49 40 42803 6602. E-mail: Wegner{at}plexus.uke.uni-hamburg.de.

Molecular and Cellular Biology, April 1999, p. 2455-2464, Vol. 19, No. 4
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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