The Internal Structure of the Oncogenic RNA Viruses

Abstract

Negative staining technique with potassium phosphotungstate (pH 7.0) was used to study the internal structure of the avian myeloblastosis virus, murine leukemia virus, murine mammary tumor virus and feline leukemia virus. Two essential structural features of the viral interior were observed: 1) single strands (30-50 A° in diameter) randomly oriented to give the appearance of a ball of yarn inside the virion; and 2) paired strands (70-90A° in diameter) that appear to be double helices which upon uncoiling give the single strands. Figs. 1 and 2 show the morphology of type B, and C particles respectively, where helical structures in the interior of the virions can be seen (arrow). The subunit structures observed on the helical regions are morphologically similar to those seen on the surface of the nucleoid that do not show helical symmetry. When helical segments were observed in the virus they were almost always seen at the periphery of the nucleoid. This is in agreement with the hollow spherical nucleoid structure of budding virions seen in thin section and suggests that the nucleocapsid is supercoiled as a hollow sphere.