Molecular characterization of a unique retrovirus associated with a fish tumor.

The walleye dermal sarcoma is a mesenchymal tumor which seasonally affects up to 27% of adult walleye fish (Stizostedion vitreum). It arises multicentrically in the dermis, in which its development remains restricted. We report the molecular cloning of a type C retrovirus from this tumor. The genome of this virus (13.2 kb) is larger than that of all retroviruses and in that respect is approximated only by the recently characterized spumaviruses. In tumors, the predominantly unintegrated linear viral DNA has a single-stranded gap region which is similar to the structure found in some lentiviruses and all spumaviruses. The presence of at least four viral transcripts suggests that this virus has the capacity to encode accessory functions and is reminiscent of the transcriptional complexity of lentiviruses and spumaviruses.