Sequence HomologyBetweentheRNA ofMason-Pfizer MonkeyVirus andtheRNA ofHumanMalignant Breast Tumors

Radioactive DNA ((3HlcDNA) complemen- tarytotheRNA ofMason-Pfizer monkeyviruswasusedin molecular hybridization experiments todemonstrate se- quencehomologybetweenitsviralRNA and RNA of human malignantbreast tumors.Hybridization products wereanalyzed bycesiumsulfate equilibrium density cen- trifugation andhydroxylapatite chromatography. Seven oftenhuman malignantbreast tumorstestedcontained virus-related RNA whenassayed byhydroxylapatite chro- matography, whereas nosequencehomologywasfoundin RNA from11humanbenignbreast tumorsorfromRNA of normalhuman spleen, liver, orkidney. Hybridizations be- tween(3H)cDNA ofthemonkeyvirusandhuman breast adenocarcinoma RNA showeda Crtl/, ofabout2 X 104. Thefidelity ofthehybrids formedwasindicated byaTmof 80.50. TheMason-Pfizer monkey virus (MPMV)wasisolated froma mammarycarcinoma ofafemale rhesus monkey(1-3). The virus hasbeensuccessfully propagated bycultivation ofthe original mammarytumorwithmonkeyembryo cells, andby cell-free infection ofmonkey, chimpanzee, orhumancells (2, 4).Avirus (X-381) morphologically indistinguishable from MPMV hasalso beenisolated fromarhesus-lactating mam- marygland biopsy (5). MPMV hasthebiochemical andbiophysical properties characteristic oftheknownRNA tumorviruses. Ithasa buoyant density of1.16g/mlinsucrose (6-8), anRNA- instructed DNA polymerase (6,9,10), anda60-70S RNA (6-8). Thishigh-molecular-weight RNA contains poly-