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Molecular and Cellular Biology, April 1999, p. 2455-2464, Vol. 19, No. 4
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.
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
*
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.
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