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J. Virol., 06 1996, 3887-3893, Vol 70, No. 6
D McVey, B Woelker and P Tegtmeyer
Previous studies have shown that phosphorylation of simian virus 40 (SV40)
T antigen at threonine 124 enhances the binding of T antigen to the SV40
core origin of replication and the unwinding of the core origin DNA via
hexamer-hexamer interactions. Here, we report that threonine 124
phosphorylation enhances the interaction of T-antigen amino acids 1 to 259
and 89 to 259 with the core origin of replication. Phosphorylation,
therefore, activates the minimal DNA binding domain of T antigen even in
the absence of domains required for hexamer formation. Activation is
mediated by only one of three DNA binding elements in the minimal DNA
binding domain of T antigen. This element, including amino acids 167, 215,
and 219, enhances binding to the unique arrangement of four
pentanucleotides in the core origin but not to other pentanucleotide
arrangements found in ancillary regions of the SV40 origin of replication.
Interestingly, the same four pentanucleotides in the core origin are
necessary and sufficient for phosphorylation-enhanced DNA binding. Further,
we show that phosphorylation of threonine 124 promotes the assembly of
high-order complexes of the minimal DNA binding domain of T antigen with
core origin DNA. We propose that phosphorylation induces conformational
shifts in the minimal DNA binding domain of T antigen and thereby enhances
interactions among T-antigen subunits oriented by core origin
pentanucleotides. Similar subunit interactions would enhance both assembly
of full-length T antigen into binary hexamer complexes and origin
unwinding.
Copyright © 1996, American Society for Microbiology
Mechanisms of simian virus 40 T-antigen activation by phosphorylation of threonine 124
Department of Molecular Genetics and Microbiology, State University of New York, Stony Brook, 11794-5222, USA.
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