The effects of some metabolic inhibitors on the ability of SV40 virus in transformed cells to be detected by cell fusion.

When mouse fibroblasts transformed by SV 40 virus are fused with African Green Monkey kidney cells about 5 % of the heterokaryons produce infective SV 40 virus. If the transformed mouse cells are treated with iododeoxyuridine before fusion, the percentage of heterokaryons producing SV40 virus is increased to between 50 and 80 %; if the transformed cells are treated with 8-azaguanine, the percentage of heterokaryons yielding virus is increased to between 59 % and 96 %. This shows that whether the SV40 virus can be detected by cell fusion depends on the state of the transformed cells beforehand. A new method for titrating SV 40 virus is described.