Investigations into the association of retroviruses with ovine lymphoma

To determine whether retroviruses are associated with sporadic ovine lymphoma, suspension cell cultures of four lymphomas and one control lymph node were labelled with tritiated uridine. Following differential and sucrose density gradient ultracentrifugation of their media a peak of radioactivity was found at a density of 1.15 to 1.18 g ml-1 in preparations from the cell cultures of two lymphomas and the normal lymph node. Sedimentation velocity centrifugation of the sodium dodecyl sulphate-treated radiolabelled material found an approximate sedimentation value of 7S. The assay for RNA directed DNA polymerase in ultracentrifuged pellets of media from cultures of 15 lymphomas and one control lymph node found activity in material from four lymphomas and the control node cultures. However, little variation in incorporation kinetics occurred with changes in assay conditions and activities were not associated with particles of density 1.15 g ml-1. It was concluded that the detected activities were not retroviral in origin.