Only a few papillomavirus types encode a short protein from the E8 gene. In the case of BPV-4 (papillomavirus genus Xi), the E8 open reading frame may substitute for the E6 open reading frame, which is absent in this papillomavirus genus.[64] These E8 genes are chemically and functionally similar to the E5 genes from some human papillomaviruses, and are also called E5/E8.