Isolation and characterization of cell clones producing various amounts of bovine leukosis virus

Several single-cell clones were isolated from lamb kidney cell line (FLK) persistently infected with bovine leukosis virus (BLV). The clones differed in the amount of produced virus, some clones were highly virus productive, others produced less virus. The restriction analysis of cell DNA from clones revealed the existence of several numbers of integrated BLV-DNA proviruses in various cell clones. In some cell clones the unintegrated proviral DNA was observed. The proviral BLV sequences were found to be integrated in reiterated DNA in some cell clones. There was no apparent relationship between the number of integrated BLV proviruses and the extent of virus production. The origin of the different numbers of integrated BLV proviruses in various cell clones is discussed.