Sequence and transcriptional analyses of the fish retroviruses walleye epidermal hyperplasia virus types 1 and 2: Evidence for a gene duplication

Walleye epidermal hyperplasia virus types 1 and 2 (WEHV1 and WEHV2, respect ively) are associated with a hyperproliferative skin lesion on walleyes tha t appears and regresses seasonally. We have determined the complete nucleot ide sequences and transcriptional profiles of these viruses. WEHV1 and WEHV 2 are large, complex retroviruses of 12,999 and 13,125 kb in length, respec tively, that are closely related to one another and to walleye dermal sarco ma virus (WDSV). These walleye retroviruses contain three open reading fram es, orfA, orfB, and orfC, in addition to gag, pal, and env. orfA and orfB a re adjacent to one another and located downstream of env. The OrfA proteins were previously identified as cyclin D homologs that may contribute to the induction of cell proliferation leading to epidermal hyperplasia and derma l sarcoma. The sequence analysis of WEHV1 and WEHV2 revealed that the OrfB proteins are distantly related to the OrfA proteins, suggesting that orfB a rose by gene duplication. Presuming that the precursor of orfA and orfB was derived from a cellular cyclin, these genes are the first accessory genes of complex retroviruses that can be traced to a cellular origin. WEHV1, WEH V2, and WDSV are the only retroviruses that have an open reading frame, orf C, of considerable size (ca. 130 amino acids) in the leader region precedin g gag. While we were unable to predict a function for the OrfC proteins, th ey are more conserved than OrfA and OrfB, suggesting that they may be biolo gically important to the viruses. The transcriptional profiles of WEHV1 and WEHV2 were also similar to that of WDSV; Northern blot analyses detected o nly low levels of the orfA transcripts in developing lesions, whereas abund ant levels of genomic, env, orfA, and orfB transcripts were detected in reg ressing lesions. The splice donors and accepters of individual transcripts were identified by reverse transcriptase PCR. The similarities of WEHV1, WE HV2, and WDSV suggest that these viruses use similar strategies of viral re plication and induce cell proliferation by a similar mechanism.