ATP stimulates the binding of simian virus 40 (SV40) large tumor antigen to the SV40 origin of replication.

A bacterial expression system was used to produce simian virus 40 large tumor antigen (T antigen) in the absence of the extensive posttranslational modifications that occur in mammalian cells. Wild-type T antigen produced in bacteria retained a specific subset of the biochemical activities displayed by its mammalian counterpart. Escherichia coli T antigen functioned as a helicase and bound to DNA fragments containing either site I or the wild-type origin of replication in a manner identical to mammalian T antigen. However, T antigen purified from E. coli did not efficiently bind to site II, an essential cis element within the simian virus 40 origin of replication. It therefore could not unwind origin-containing plasmids or efficiently replicate simian virus 40 DNA in vitro. The ability of protein phosphorylation to modulate the intrinsic preference of full-length T antigen for either site I or site II is discussed.

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Simian virus 40 (SV40) large tumor antigen causes stepwise changes in SV40 origin structure during initiation of DNA replication.

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.86.11.3939 ◽

1989 ◽

Vol 86 (11) ◽

pp. 3939-3943 ◽

Cited By ~ 23

Author(s):

J. M. Roberts

Keyword(s):

Dna Replication ◽

Tumor Antigen ◽

Simian Virus 40 ◽

Simian Virus ◽

Large Tumor ◽

Large Tumor Antigen ◽

Sv40 Origin ◽

Initiation Of Dna Replication

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Nonselective expression of simian virus 40 large tumor antigen fragments in mouse cells.

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.79.6.2064 ◽

1982 ◽

Vol 79 (6) ◽

pp. 2064-2067 ◽

Cited By ~ 8

Author(s):

V. B. Reddy ◽

S. S. Tevethia ◽

M. J. Tevethia ◽

S. M. Weissman

Keyword(s):

Tumor Antigen ◽

Simian Virus 40 ◽

Simian Virus ◽

Large Tumor ◽

Large Tumor Antigen ◽

Mouse Cells

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Prostate and mammary adenocarcinoma in transgenic mice carrying a rat C3(1) simian virus 40 large tumor antigen fusion gene.

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.91.23.11236 ◽

1994 ◽

Vol 91 (23) ◽

pp. 11236-11240 ◽

Cited By ~ 223

Author(s):

I. G. Maroulakou ◽

M. Anver ◽

L. Garrett ◽

J. E. Green

Keyword(s):

Transgenic Mice ◽

Tumor Antigen ◽

Fusion Gene ◽

Simian Virus 40 ◽

Simian Virus ◽

Mammary Adenocarcinoma ◽

Large Tumor ◽

Large Tumor Antigen

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Differential roles of heat shock protein 70 in the in vitro nuclear import of glucocorticoid receptor and simian virus 40 large tumor antigen

Molecular and Cellular Biology ◽

10.1128/mcb.14.8.5088-5098.1994 ◽

1994 ◽

Vol 14 (8) ◽

pp. 5088-5098

Author(s):

J Yang ◽

D B DeFranco

Keyword(s):

Heat Shock ◽

Heat Shock Protein ◽

Tumor Antigen ◽

Nuclear Import ◽

Simian Virus 40 ◽

Simian Virus ◽

Large Tumor ◽

Large Tumor Antigen ◽

Cell Cytosol

Nuclear import of glucocorticoid receptors (GRs) was analyzed in vitro with digitonin-permeabilized cells (S. A. Adam, R. Sterne-Marr, and L. Gerace, J. Cell Biol. 111:807-816, 1990). Indirect immunofluorescence methods were used to monitor the transport of GRs from rat hepatoma and fibroblast cell cytosol into HeLa nuclei. In vitro nuclear import of GRs was shown to be hormone dependent and to require ATP and incubation at ambient temperatures (i.e., 30 degrees C). Hormone-dependent dissociation of GR-bound proteins, such as the 90-kDa heat shock protein, hsp90, is part of an activation process that is obligatory for the expression of the receptor's DNA-binding activity. Inhibition of in vitro GR activation by Na2MoO4 blocked hormone-dependent nuclear import, demonstrating that receptor activation is required for nuclear import. The addition to GR-containing cytosol of antiserum directed against the cytosolic 70-kDa heat shock protein, hsp70, while effective in blocking the nuclear import of simian virus 40 large tumor antigen (SV40 TAg), did not affect hormone-dependent nuclear import of endogenous, full-length GRs or an exogenously added truncated GR protein (i.e., XGR556) that lacks a hormone-binding domain but possesses a constitutively active nuclear localization signal sequence (NLS). Depletion of hsp70 from HeLa cell cytosol did not affect the nuclear import of exogenously added XGR556 but led to inhibition of SV40 TAg nuclear import. Thus, two closely related NLSs, one contained within GRs and the other contained within SV40 TAg, are distinguished by their differential requirements for hsp70 in vitro.

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