THE aetiological role of RNA tumour viruses in mammary cancer of experimental animals coupled with observations of morphologically similar particles in human milk1,2 has motivated considerable interest in the biological role of these virions in man. The specificity and sensitivity of the simultaneous detection test3 for reverse transcriptase (RT) which requires that the viral enzyme polymerise radioactive DNA using endogenous 70S and/or 35S viral DNA as template, suggested its usefulness for the detection of RNA tumour viruses in human milk4. In two recent studies2,5 comparing the detection of such virions in human milk by electron microscopy (negative staining) with the detection of RT activity, no correlation was observed. As a part of our effort at relating the presence of such virions in human milk to a familial history of breast cancer, we employed reconstruction experiments to determine the reliability of the simultaneous detection test for the routine testing of human milk samples for the presence of RNA tumour viruses. Analysis of the products of the reaction was carried out by the use of gel electrophoresis instead of by velocity gradients6. This method offers the advantage that, in addition to the 70S and/or 35S viral peak, it also detects a 4S peak which represents the DNA products of the reaction which are free from the large molecular weight viral RNA.
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McCORMICK, J., LARSON, L. & RICH, M. RNase inhibition of reverse transcriptase activity in human milk. Nature 251, 737–740 (1974). https://doi.org/10.1038/251737a0
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