Evolution of type C viral genes: preservation of ancestral murine type C viral sequences in pig cellular DNA

Abstract

Domestic pigs (Sus scrofa) and other members of the family Suidae have multiple copies of type C viral gene sequences in the cellular DNA of all their tissues. Partially homologous viral gene sequences are also found in cellular DNA of rodents, particularly Muridae. The results lead to the conclusion that type C viral genes were introduced into the Suidae lineage as a result of trans-species infection by an ancestral xenotropic murine virus. The rate of evolution of the virogene sequences in the pig appears to be much slower than that of genes that have remained in the rodent lineage; this may be a consequence of transfer from a shorter-lived animal (the rodent) to a longer-lived one (the pig). We estimate the time of gene transmission as 5-10 million years ago and conclude that the present-day porcine type C virogenes most closely approximate the viral genes as they were several million years ago in the rodent lineage.