Abstract
Proviral DNA transcribed from the RNA of Moloney murine sarcoma virus was isolated from newly infected cells. Three forms of viral DNA were observed: (i) a linear double-stranded form of 3.4 X 10(6) daltons which constituted the major viral DNA species in the cell, and is thought to be a complete transcript (monomer) of viral RNA; (ii) a fast-sedimenting viral DNA bigger than the monomeric unit which can be either integrated provirls or concatamers; and (iii) covalently closed circles of monomer size representing 5% or less of the total viral DNA in the cell. The linear viral DNA was tested for its susceptibility to restriction endonucleases by electrophoretic analysis of the digestion products and their identification by hybridization with viral RNA or cDNA probes. The linear DNA is not cleaved by endonucleases EcoRI and BamHI. It is cleaved into two fragments by endonucleases HindIII and Hae II, and into three fragments by restriction endonuclease HincII. The fragments of the viral DNA added up to approximately 3.4 X 10(6) daltons; this and the uniform size of the linear DNA indicated that the viral DNA has unique ends and a complexity of 3.4 X 10(6) daltons. The different cleavage fragments were ordered with respect to each other and the 3' end of the viral RNA. It was observed that fragments from both ends of the linear DNA can be hybridized to sequence(s) at the 3' end of murine sarcoma virus RNA; this result suggested the possibility that a short redundant sequence exists at both termini of the genome.