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Journal of Virology, January 1999, p. 260-269, Vol. 73, No. 1
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
The Adeno-Associated Virus Type 2 Regulatory
Proteins Rep78 and Rep68 Interact with the Transcriptional
Coactivator PC4
Stefan
Weger,1,2
Meike
Wendland,2
Jürgen A.
Kleinschmidt,3 and
Regine
Heilbronn1,2,*
Institut für Infektionsmedizin,
Abteilung Virologie, Freie Universität Berlin, D-12203
Berlin,1
Max-Planck-Institut
für Biochemie, D-82152 Martinsried,2 and
Deutsches Krebsforschungszentrum, Forschungsschwerpunkt
Angewandte Tumorvirologie, D-69120 Heidelberg,3
Germany
Received 22 July 1998/Accepted 12 October 1998
The adeno-associated virus type 2 (AAV-2) Rep78/Rep68 regulatory
proteins are pleiotropic effectors of viral and cellular DNA
replication, of cellular transformation by viral and cellular oncogenes, and of homologous and heterologous gene expression. To
search for cellular proteins involved in mediating these functions, we
used Rep68 as bait in the yeast two-hybrid system and identified the
transcriptional coactivator PC4 as a Rep interaction partner. PC4 has
been shown to mediate transcriptional activation by a variety of
sequence-specific transcription factors in vitro. Rep amino acids 172 to 530 were sufficient and amino acids 172 to 224 were absolutely
necessary for the interaction with PC4. The PC4 domains required for
interaction were mapped to the C-terminal single-stranded DNA-binding
domain of PC4. In glutathione S-transferase (GST) pull-down
assays, in vitro-transcribed and -translated Rep78 or Rep68 proteins
were bound specifically by GST-PC4 fusion proteins. Similarly, PC4
expressed in Escherichia coli was bound by GST-Rep fusion
proteins, confirming the direct interaction between Rep and PC4 in
vitro. Rep was found to have a higher affinity for the
nonphosphorylated, transcriptionally active form of PC4 than for
the phosphorylated, transcriptionally inactive form. The latter is
predominant in nuclear extracts of HeLa or 293 cells. In the yeast
system, but not in vitro, Rep-PC4 interaction was disrupted by a point
mutation in the putative nucleotide-binding site of Rep68, suggesting
that a stable interaction between Rep and PC4 in vivo is ATP dependent.
This mutation has also been shown to impair Rep function in AAV-2 DNA
replication and in inhibition of gene expression and inducible DNA
amplification. Cytomegalovirus promoter-driven overexpression of PC4
led to transient accumulation of nonphosphorylated PC4 with concomitant
downregulation of all three AAV-2 promoters in the absence of helper
virus. In the presence of adenovirus, this effect was relieved. These
results imply an involvement of the transcriptional coactivator PC4 in
the regulation of AAV-2 gene expression in the absence of helper virus.
*
Corresponding author. Mailing address: Institut
für Infektionsmedizin, Abteilung Virologie, Freie
Universität Berlin, Hindenburgdamm 27, 12203 Berlin, Germany.
Phone: (49) 30 8445 3696. Fax: (49) 30 8445 4485. E-mail:
heilbronn{at}ukbf.fu-berlin.de.
Journal of Virology, January 1999, p. 260-269, Vol. 73, No. 1
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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