Identification of a novel type C porcine endogenous retrovirus: evidence that copy number of endogenous retroviruses increases during host inbreeding

Different classes of porcine endogenous retroviruses (PERVs), which have th e potential to infect humans during xenotransplantation, have been isolated from the pig genome. Because vertebrate genomes may contain numerous endog enous retrovirus sequences, the pig genome was examined for additional endo genous retroviruses, resulting in the isolation of a novel, complete endoge nous retrovirus genome, designated PERV-E. The gag, pol and env genes of PE RV-E are closely related to those of human endogenous retrovirus (HERV) 4-1 , which belongs to the HERV-E family. Results of stud ies to determine the presence and copy number of PERVs demonstrated that PERV-E and PERV-A/B-lik e proviruses were present in all genomes tested, but that PERV-C was not fo und in two of the species examined, including wild boar. Multiple copies of PERVs could be found in each pig genome. Among all of the pig genomes test ed, the wild boar genome had the lowest copy number of all PERVs, suggestin g that the number of integrations of complete endogenous retroviruses is in creased by inbreeding.