No abstract

The ultrastructure (1) and many of the characteristics of the biological activities of measles virus (2--5) indicate that it should be classified as belonging to the group of large myxoviruses. It is therefore to be expected that in further analogy it should contain ribonucleic acid (RNA), but no deoxyribonucleic acid (DNA). This was also suggested on the basis of results (6, 7) demonstrating that inhibition of cellular DNA synthesis by the nucleic acid analogue 5-fluorodeoxyuridinc did not suppress the multiplication of measles virus. In order to obtain more direct evidence for the type of nucleic acid present in measles virus the following two types of experiments were performed: 1. Virus multiplication was allowed to take place in the presence of medium containing Ha-thymidine or H3-uridine plus unlabelled thymidine. Material was harvested at an advanced stage of degeneration and concentrated 10 times by forced dialysis. A semi-purified preparation of intact and almost intact virus particles was then prepared by differential centrifugation. The effect on the radioacti~dty of adsorption with monkey erythrocytes of such preparations either untreated or after treatment with Tween 80 and ether was analyzed. A considerable fraction of the I-I3-uridine incorporated into the RNA in untreated material was removed by the adsorption. No radioactivity was removed if the preparations previous to adsorption had been treated with Tween 80 and ether or if, instead, Ha-thymidine had been used for labelling.2. Preparations of semi-purified intact and almost intact virus particles were also submitted to equilibrium centrifugation in CsC1 gradients with an average density of 1.23 g/cc. The biological activities and content of nucleic acids at various densities were analyzed. RNA and DNA were determined colorimetrically or by the isotope labelling technique described above. A correlation was found between biological activities and accumulation of I%NA at densities of 1.22 to 1.25 g/cc.