In vitro synthesis of a 9 kbp terminally redundant DNA carrying the infectivity of Moloney murine leukemia virus.

Detergent-disrupted virions of Moloney murine leukemia virus synthesize a 9 kbp double-stranded infectious DNA. It contains mainly full-length, single-stranded DNA, and its infectivity and size are insensitive to digestion by the single-strand-specific S1 nuclease. Analysis of fragmentation of the DNA using restriction endonucleases has shown that it is indistinguishable from the linear double-stranded DNA synthesized in infected cells. On the basis of the positions of the cleavage sites for a number of enzymes, the 9 kbp DNA has a 575 base direct terminal repetition. It is longer than the viral RNA at both ends, evidently due to repetitive copying of segments of the RNA. Virions also synthesize an 8.4 kbp double-stranded circular DNA that lacks one copy of the terminal repetition, as well as viral DNA longer than 9 kbp. The enzymatic machinery in the virions of retroviruses therefore appears to be responsible for all the steps involved in making fully double-stranded linear and one form of circular DNA.