NUCLEOTIDE-SEQUENCE AND PROTEIN-ANALYSIS OF A COMPLEX PISCINE RETROVIRUS, WALLEYE DERMAL SARCOMA-VIRUS

Walleye dermal sarcoma virus (WDSV) is a fish retrovirus associated wi th the development of tumors in walleyes. We have determined the compl ete nucleotide sequence of a DNA clone of WDSV, the N-terminal amino a cid sequences of the major proteins, and the start site for transcript ion. The long terminal repeat is 590 bp in length, with the U3 region containing consensus sequences likely to be involved in viral gene exp ression. A predicted histidyl-tRNA binding site is located 3 nucleotid es distal to the 3' end of the long terminal repeat, Virus particles p urified by isopycnic sedimentation followed by rate zonal sedimentatio n showed major polypeptides with molecular sizes of 90, 25, 20, 14 and 10 kDa, N-terminal sequencing of these allowed unambiguous assignment of the small polypeptides as products of the gag gene, including CA a nd NC, and the large polypeptide as the TM product of env. The 582-ami no-acid (aa) Gag protein precursor is predicted to be myristylated as is found for most retroviruses. NC contains a single Cys-His motif lik e those found in all retroviruses except spumaviruses. The WDSV pro an d pol genes are in the same translational reading frame as gag and thu s apparently are translated after termination suppression, The env gen e encodes a surface (SU) protein of 469 aa predicted to be highly glyc osylated and a large transmembrane (TM) protein of 754 aa. The sequenc e of TM is unusual in that it ends in a very hydrophobic segment of 65 residues containing a single charged residue. Following the env gene are two nonoverlapping long open reading frames of 290 aa (orf-A) and 306 aa (orf-C), neither of which shows significant sequence similarity with known genes. A third open reading frame of 119 aa (orf-C) is loc ated in the leader region preceding gag. The predicted amino acid sequ ence of reverse transcriptase would place WDSV phylogenetically closes t to the murine leukemia virus-related genus of retroviruses. However, other members of this genus do not have accessory genes, suggesting t hat WDSV acquired orf-A, orf-B, and perhaps orf-C late in its evolutio n. We hypothesize by analogy with other complex retroviruses that the accessory genes of WDSV function in the regulation of transcription an d in RNA processing acid also in the induction of walleye dermal sarco ma.