Biological activity of cloned Moloney sarcoma virus DNA: Terminally redundant sequences may enhance transformation efficiency.

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Abstract
The ability of cloned restriction fragments containing the whole and partial genomes of 2 strains of Moloney murine sarcoma virus to induce cell transformation in DNA transfection assays was measured. The cloned intact ml and HTl murine sarcoma virus proviruses transform with an efficiency of .apprxeq. 40,000-50,000 focus-forming units/pmol of proviral DNA, and the majority of these transformed [mouse fibroblast NIH 3T3] cells contain a rescuable viral genome. A cloned 2.1-kilobase-pair internal fragment of the murine sarcoma virus containing 1.2 kilobase pairs of sarcoma virus-specific sequences (src) and .apprxeq. 900 base pairs of leukemia virus-derived sequences adjacent to the 5'' end of src transforms with approximately 1/10,000th the efficiency of the intact genome. When leukemia virus-derived sequences containing a single copy of the 600-base-pair direct terminal repeated sequences are present at either the 5'' or 3'' end of this src-containing fragment, the transforming activity is stimulated 1000-fold. Cotransfection with a mixture of cloned fragments, one containing the internal 2.1-kilobase-pair src fragment and the other containing a single copy of the terminally redundant sequence, results in a 300-fold increase in transformation efficiency.