Abstract
A murine leukaemia virus helper-independent strain of Moloney sarcoma virus (MSV), designated S + L -, was isolated from cells transformed by MSV in the absence of replicating leukaemia virus. The virus is non-infectious in tissue culture as evidenced by its failure to replicate in a variety of murine cell lines.
Sucrose gradient and gel electrophoretic analyses of the purified S + L - isolate showed that the virus contains 60 to 70 S RNA. The virus also possesses RNA-dependent DNA polymerase (RDDP) activity.
On the basis of these data it would appear that factors other than high mol. wt. RNA and RDDP may account for the lack of infectivity of this strain of MSV.