Abstract
The structure and arrangement of the multiple provirus copies of avian sarcoma virus in a rat XC cell line were studied by restriction endonucleases. The following observations were made: (i) the majority of the proviruses integrated randomly with respect to cell DNA; (ii) no gross deletions or rearrangements in the proviruses were observed; (iii) two types of proviruses (type I and type II) could be distinguished on the basis of restriction endonuclease cleavage sites; (iv) the virus rescued from these cells was derived from type II provirus, which has a novel EcoRI site between the env and pol genes; (v) most of the provirus units contained the src gene.