Binding to retinoblastoma pocket domain does not alter the inter-domain flexibility of the J domain of SV40 large T antigen

► The data reveal flexible linkage of origin binding and J domains of SV40 T antigen. ► Contacts between J domain and pRb in the crystal structure are transient in solution. ► The origin binding domain remains dynamically independent in the complex with pRb. ► The results support a 'chaperone' model for the action of the J domain.