THE INITIATOR PROTEIN-E1 BINDS TO THE BOVINE PAPILLOMAVIRUS ORIGIN OFREPLICATION AS A TRIMERIC RING-LIKE STRUCTURE

The replication initiator protein El binds to the origin of replicatio n of bovine papillomavirus in several forms. El can bind to its recogn ition sequence as a monomer together with the viral transcription fact or E2, or as a trimeric El complex. The trimerization of El is mediate d by the sequence-specific binding of El to DNA, and results in an El complex that is linked topologically to the DNA because the three mole cules of El form a ring-like structure that encircles the DNA. These r esults demonstrate that El utilizes unusual mechanisms for sequence-sp ecific binding to DNA and for the generation of a structure that encir cles the DNA. We believe that these forms of El bound to the origin of replication represent intermediates in a transition in the function o f El, from a sequence-specific origin of replication recognition prote in to a form of El that is competent for the initiation of viral DNA r eplication.