Construction and isolation of a transmissible retrovirus containing the src gene of Harvey murine sarcoma virus and the thymidine kinase gene of herpes simplex virus type 1

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Abstract
.lambda. recombinants containing the Harvey murine sarcoma virus genome and the thymidine kinase (tk) gene of herpes simplex virus type 1 linked to each other were constructed. The tk gene was located in a position downstream from both the long terminal repeat and the src gene of Harvey murine sarcoma virus. The DNA of the .lambda. recombinants were used to transfect NIH3T3 mouse fibroblasts to obtain Harvey murine sarcoma virus DNA-induced foci of transformed cells. The transformed foci were superinfected with a helper-independent retrovirus and new individual retroviruses were isolated from the superinfected foci. The new viruses could induce focus formation on NIH3T3 cells and could convert NIH3T3(TK-) cells into TK+ cells by carrying the herpes simplex virus type 1 tk gene into the TK- cells. From virus-infected cells, nonproducer foci were isolated on NIH3T3 cells and TK+ transformants on NIH3T3(TK-) cells containing 1 such new viral genome coding for the dual properties. The new retroviral sequence in the nonproducer cells could be rescued into virus particles at high titers by superinfection with a helper-independent retrovirus. A hybridization analysis indicated that the recombinant virus contained both the Harvey murine sarcoma virus src sequence and the tk gene sequence in a single RNA species .apprx. 4.9 kilobases long. Retroviruses can be used as true vectors for genes other than genes that lead to oncogenesis.