Restriction analysis of additional "non-producing" cell clones obtained after transformation of Japanese quail fibroblasts with viruses rescued from cryptovirogenic H-19 cells.

The proviral structure of two transforming viruses rescued from cryptovirogenic H-19 hamster cells harbouring the LTR, v-src, LTR proviral structure was analysed by restriction mapping. It was established that the rescued G8 virus keeps the same restriction pattern as that observed in the cryptic H-19 provirus and that it is integrated into the cell genome at a different position characteristic of each "non-producing" (NP) cell clone. In these features it corresponds to the previously described F6 rescued virus. In studying the E6 rescued virus we found again that it is integrated at a position characteristic of the NP cell line studied. Using a series of restriction enzymes it was specified that the E6 proviral unit acquired at least 0.25 kb from the left part of the gag gene and 0.85 kb of an unidentified DNA. Because this DNA structure was not digested with the enzymes employed that cut in RSV provirus and did not hybridize with the viral gene probes, it might be of cellular origin. The recombinational events involved in E6 virus genesis, the nature of an additional DNA structure, and the functional significance of the acquired part of the gag gene are discussed.