Two Regions of Simian Virus 40 T Antigen Determine Cooperativity of Double-Hexamer Assembly on the Viral Origin of DNA Replication and Promote Hexamer Interactions during Bidirectional Origin DNA Unwinding

摘要: Phosphorylation of simian virus 40 large tumor (T) antigen on threonine 124 is essential for viral DNA replication. A mutant T (T124A), in which this was replaced by alanine, has helicase activity, assembles double hexamers viral-origin DNA, and locally distorts the origin structure, but it cannot catalyze unwinding. class T-antigen mutants with single-amino-acid substitutions binding domain (class 4) remarkably similar properties, although these proteins are phosphorylated 124, as we show here. By comparing properties T124A 4 those wild type, demonstrate that bind to reduced cooperativity. We report subunits impair ability containing wild-type protein unwind suggesting interactions between also required Moreover, antigens display dominant-negative inhibition replication activity protein. propose hexamers, mediated through N-terminal region antigen, play a role double-hexamer assembly speculate one surface each subunit hexamer may form docking site can interact other hexamer, either directly or another regulated phosphorylation.