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

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Abstract
Domestic pigs (Sus scofa) and other members of Suidae have multiple copies of type C viral gene sequences in the cellular DNA of their tissues. Partially homologous viral gene sequences are also found in cellular DNA of rodents, particularly Muridae. Type C viral genes were probably 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 remained in the rodent lineage; this may be a result of transfer from a shorter-lived animal (the rodent) to a longer-lived one (the pig). The estimated time of gene transmission is 5-10 million years ago. The present-day porcine type C virogenes ["fossil" genes] closely approximate the viral genes as they were several million years ago in the rodent lineage.