Abstract
Endogenous Borna-like nucleoprotein (EBLNs) elements were recently discovered as non-retroviral RNA virus elements in genomes of various mammalian species. Although most of EBLNs appeared to be defective, the primate EBLNs encoded an ORF with an equivalent length to nucleoprotein of borna disease virus, and expressed as mRNA in several primate cell lines, suggesting that primate EBLNs may encode proteins that perform biological functions in the host. In order to verify whether primate EBLNs have encoded functional protein during evolution of primates, the present study examined the natural selection operating on the ORFs encoded by primate EBLNs. Although negative selection was detected on the ORFs encoded by ancestral EBLN before the divergence of Old World and New World monkeys, no natural selection was detected on the ORFs encoded by primate EBLNs. These results suggest that although the primate EBLNs had encoded some functional protein more than 40 million years ago, the function retained in the ancestral primate EBLN may have been lost due to the relaxation of functional constraint during evolution of primates.