The amino-terminal transforming region of simian virus 40 large T and small t antigens functions as a J domain.
Simian virus 40 (SV40) encodes two proteins, large T antigen and small t antigen that contribute to virus-induced tumorigenesis. Both proteins act by targeting key cellular regulatory proteins and altering their function. Known targets of the 708-amino-acid large T antigen include the three members of the retinoblastoma protein family (pRb, p107, and p130), members of the CBP family of transcriptional adapter proteins (cap-binding protein [CBP], p300, and p400), and the tumor suppressor p53. Small t antigen alters the activity of phosphatase pp2A and transactivates the cyclin A promoter. The first 82 amino acids of large T antigen and small t antigen are identical, and genetic experiments suggest that an additional target(s) important for transformation interacts with these sequences. This region contains a motif similar to the J domain, a conserved sequence found in the DnaJ family of molecular chaperones. We show here that mutations within the J domain abrogate the ability of large T antigen to transform mammalian cells. To examine whether a purified 136-amino-acid fragment from the T antigen amino terminus acts as a DnaJ-like chaperone, we investigated whether this fragment stimulates the ATPase activity of two hsc70s and discovered that ATP hydrolysis is stimulated four- to ninefold. In addition, ATPase-defective mutants of full-length T antigen, as well as wild-type small t antigen, stimulated the ATPase activity of hsc70. T antigen derivatives were also able to release an unfolded polypeptide substrate from an hsc70, an activity common to DnaJ chaperones. Because the J domain of T antigen plays essential roles in viral DNA replication, transcriptional control, virion assembly, and tumorigenesis, we conclude that this region may chaperone the rearrangement of multiprotein complexes.
Srinivasan
A
A
Department of Biological Sciences, University of Pittsburgh, Pennsylvania 15260, USA.
McClellan
A J
AJ
Vartikar
J
J
Marks
I
I
Cantalupo
P
P
Li
Y
Y
Whyte
P
P
Rundell
K
K
Brodsky
J L
JL
Pipas
J M
JM
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D002460:Cell Line; D002472:Cell Transformation, Viral / Q000235:genetics*; D017124:Conserved Sequence / Q000235:genetics; D016213:Cyclins / Q000235:genetics; D005347:Fibroblasts; D005656:Fungal Proteins / Q000378:metabolism; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D011506:Proteins; D051381:Rats; D016160:Retinoblastoma Protein / Q000378:metabolism; D050720:Retinoblastoma-Like Protein p107; D050717:Retinoblastoma-Like Protein p130; D029701:Saccharomyces cerevisiae Proteins; D013539:Simian virus 40 / Q000276:immunology*; D015534:Trans-Activators / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
D000952:Antigens, Polyomavirus Transforming; D016213:Cyclins; D005656:Fungal Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D009687:Nuclear Proteins; D010750:Phosphoproteins; D011506:Proteins; C489485:Rbl1 protein, mouse; C493838:Rbl2 protein, mouse; C493839:Rbl2 protein, rat; D016160:Retinoblastoma Protein; D050720:Retinoblastoma-Like Protein p107; D050717:Retinoblastoma-Like Protein p130; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D016159:Tumor Suppressor Protein p53; C070319:YDJ1 protein, S cerevisiae; D010749:Phosphoprotein Phosphatases; D000251:Adenosine Triphosphatases; C095973:SSA1 protein, S cerevisiae