Sequence Homology of Nucleic Acids from Human Breast Cancer Cells and Complementary DNA's from Murine Mammary Tumor Virus and Mason-Pfizer Monkey Virus¹

Simultaneous presence of murine mammary tumor virus- and Mason-Pfizer monkey virus-specific sequences has been detected in nucleic acids isolated from some human breast tumors and from MCF-7 cells, a well-characterized human breast cancer cell line. Carefully characterized long complementary DNA transcripts were used in the molecular hybridization experiments. From the data that are presently available, it would appear that when homology is detected with one of the mammary tumor probes the other also generally shows homology. Among all the complementary DNA-RNA hybrids only three, all murine mammary tumor virus hybrids, show T_m values close to 80°. The rest of the hybrids are low melting with shallow slopes for their C_rt curves, indicating partial and imperfect hybrids in the majority of cases. Low levels of weak hybrid formation are also detectable with the tumor DNA's. The present experiments cannot ascertain whether the hybridizing sequences from Mason-Pfizer monkey virus and murine mammary tumor virus code for specific viral functions in their natural hosts. Annealing experiments using gene specific cDNA's would be required for fully characterizing these sequences.