BOVINE PAPILLOMAVIRUS TYPE-1 GENOMES AND THE E2 TRANSACTIVATOR PROTEIN ARE CLOSELY ASSOCIATED WITH MITOTIC CHROMATIN

The bovine papillomavirus type 1 E2 transactivator protein is required for viral transcriptional regulation and DNA replication and may be i mportant for long-term episomal maintenance of viral genomes within re plicating cells (M. Piirsoo, E. Ustav, T. Mandel, A.Stenlund, and M. U stav, EMBO J. 15:1-11, 1996). We have evidence that, in contrast to mo st other transcriptional transactivators, the E2 transactivator protei n is associated with mitotic chromosomes in dividing cells. The shorte r E2-TR and E8/E2 repressor proteins do not bind to mitotic chromatin, and the N-terminal transactivation domain of the E2 protein is necess ary for the association. However, the DNA binding function of E2 is no t required. We have found that bovine papillomavirus type 1 genomes ar e also associated with mitotic chromosomes, and we propose a model in which E2-bound viral genomes are transiently associated with cellular chromosomes during mitosis to ensure that viral genomes are segregated to daughter cells in approximately equal numbers.