Document Detail

Phosphorylation downregulates the DNA-binding activity of simian virus 40 T antigen.
MedLine Citation:
PMID:  3023678     Owner:  NLM     Status:  MEDLINE    
Proteolytic fragments of simian virus 40 tumor (T) antigen and T antigen that was dephosphorylated with alkaline phosphatase bound between 1.5 to 2 times more origin-containing simian virus 40 DNA than did intact T antigen in DNA saturation experiments. Kinetic experiments showed that these treatments also enhanced the rate at which T antigen bound to the DNA. The enhanced binding of T-antigen fragments correlated with the generation of DNA-binding fragments that lacked the NH2-terminal region. Dephosphorylation of T antigen in vitro resulted in the removal of phosphate groups from the NH2-terminal region as well as from the COOH-terminal region. To test the effects of dephosphorylation on the size of the protein, immunoaffinity-purified T antigen was subjected to sedimentation with and without prior treatment with alkaline phosphatase. Most of the purified protein sedimented as a monomer and no significant effect was observed after dephosphorylation, indicating that the enhanced DNA-binding activity was probably not due to the uncovering of additional binding sites buried specifically in oligomerized T antigen. Taken together, these results indicate that in vivo phosphorylation of the NH2-terminal region (residues 106 to 124) decreases the binding of the protein to the DNA origin. The effect is reversed by in vitro dephosphorylation or by proteolysis which removes the highly phosphorylated NH2-terminal arm of the polypeptide. We suggest that phosphorylation inactivates one of two distinct DNA-binding activities on the polypeptide chain perhaps corresponding to two separate regions in T antigen.
D T Simmons; W Chou; K Rodgers
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Journal of virology     Volume:  60     ISSN:  0022-538X     ISO Abbreviation:  J. Virol.     Publication Date:  1986 Dec 
Date Detail:
Created Date:  1986-12-29     Completed Date:  1986-12-29     Revised Date:  2009-11-18    
Medline Journal Info:
Nlm Unique ID:  0113724     Medline TA:  J Virol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  888-94     Citation Subset:  IM    
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MeSH Terms
Antigens, Viral, Tumor / metabolism*
DNA-Binding Proteins / metabolism*
Gene Expression Regulation
Peptide Fragments / metabolism
Phosphoproteins / metabolism
Simian virus 40 / genetics*,  immunology
Structure-Activity Relationship
Viral Proteins / metabolism*
Grant Support
Reg. No./Substance:
0/Antigens, Viral, Tumor; 0/DNA-Binding Proteins; 0/Peptide Fragments; 0/Phosphoproteins; 0/Viral Proteins

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