SUMO-1 modification of bovine papillomavirus E1 protein is required for intranuclear accumulation

The El protein is a multifunctional, origin-binding helicase that is essential for replication of papillomaviruses. Recently, bovine papillomavirus El was shown to be post-translationally modified by the addition of the SUMO-1 polypeptide, Here we show that the site of sumoylation maps to lysine residue 514. This lysine and the flanking sequences are well conserved in human papillomavirus (HPV) El proteins. Both HPV1a and HPV18 El proteins are substrates for sumoylation in vitro, which is consistent with this modification being a general property of El proteins. Mutations, which impair the sumoylation of bovine papillomavirus El, prevent normal nuclear accumulation of El with a concomitant loss of replication capacity. These results suggest that sumoylation plays a role in nuclear transport and could regulate the El replication function by controlling access to the nuclear replication domains.