RNA-directed DNA-polymerase activity in Greene hamster melanoma.

The present investigation is concerned with the search for RNA-directed DNApolymerase activity in human and hamster melanoma cells in both in vivo tumors and tumor cells grown in tissue culture. The assays and techniques employed are based upon model studies carried out in this laboratory with the enzyme from avian myeloblastoses virus, and feline sarcoma, and lymphoma virus. In recent years, several workers have found what appear to be virus-like particles of considerable interest in animal melanomas; and similar particles are being sought in human ocular and skin melanomas although none has as yet been reported. New methods for the biochemical investigation of the mechanism of reproduction of RNA tumor viruses were opened when Temin and Mizutani (1) and Baltimore (2) reported findings of an enzyme present in RNA tumor virus which could use an RNA template to catalyze the formation of DNA. Detection of this enzyme provides a marker for the identification of the virus itself. The enzyme can be thought of as the "fobtprint" of the virus, since it is possible that the enzyme and the DNA which code for the virus could be present, but the virus is not present as a morphologic entity. The enzyme activity also provides a more sensitive, if less definitive, assay for virus particles than techniques such as electron microscopy. Thus, if animal and human melanomas were caused by an RNA tumor virus which carried the enzyme RNA-directed DNA-polymerase, the enzyme assay would appear to be a logical first step toward detecting its presence.