Emerging Viruses-Aids & Ebola - By Leanard ... - preterhuman.net

STRINGNER S. YANGROBERT C. TINGBionetics Research Laboratories,Bethesda, Maryland 20014An RNA dependent DNA polymerase analogous to that of RNAtumour viruses has been found in lymphoblasts of leukaemicpatients but not of normal donors. The enzyme can use an RNAtemplate from mammalian cells to synthesize DNA.RECENT reports by Temin and Baltimore that an RNAdependent DNA polymerase activity is present in oncogenicANA viruses, now confirmed and extended in other laboratoriesprovide a mechanism by which an RNA virus may insert stablegenetic information into a host cell genome.The aetiology of human acute leukaemia is not known, but a rolefor RNA oncogenic viruses in human neoplasia has beenproposed for several reasons. Although RNA virus particles havenot been clearly accociated with human leukaemia, we haveexamined human leukaemic cells for the presence of an RNAdependent DNA polymerase because: (1) it is possible that RNAVirus particles are regularly present in human leukaemic cells butcannot be detected by ordinary means. The presence of a uniqueenzyme might be a more sensitive index. (2) The virus particlesmay never be formed but the viral genome would be integratedand undetected, yet functional in the host cell. The enzyme couldbe required for subsequent formation of additional viral DNAused in infection of other host cells. (3) Information flow fromRNA to DNA raises interesting questions regarding geneamplification during biochemical cytodifferentiation. Thismechanism could have considerable implications forcell growth and differentiation, and because human leukaemiahas been considered a disorder of celll differentiatio, it may alsohave implications for leukaemogenesis"'.Choice and Preparation of CellsSeveral considerations influenced our choice of cells. First, acuteleukaemia was selected rather than the chronic form because thecharacteristics of the former cell type are more malignant andless often contaminated with other types of leucocytes. Inleukaemia of an acute "blastic" type, a population of almost 100per cent blasts can be obtined directly from a patient. Second, thelymphoblastic type was chosen rather than the myeloblastic(granulocytic type) because the latter are more likely to beaccociated with other more differentiated cells of the myeloid(granulocytic) series. These cells contain abundant lysosomeswith high nuclease activities, making any RNA analysis orpolymerase assay extremely difficult. Third, proliferativelymphoblasts can also be obtained from normal humanvolunteers. This is achieved by transformation of normal