On the use of chloramine-T to iodinate specifically the surface proteins of intact enveloped viruses.

Rous-associated virus-6I was used as a model for studying the labelling specificity of the chloramine-T iodination procedure when applied to intact enveloped viruses. The specificity of labelling depended markedly on the concentration of iodide in the reaction mixture. At low concentrations of iodide (below 0-5 muM) only the surface proteins and lipid of intact virions were iodinated; there was no detectable labelling of internal proteins. At 10 muM-iodide, however, both internal and external proteins were iodinated; moreover there was a marked change in the reactivity of the surface proteins. It appears that the lipid envelope provides an effective barrier to the iodinating complex generated at low, but not at high, concentrations of iodide. These and other observations suggest that the chloramine-T procedure has a previously unrecognized potential for specifically labelling the surface proteins of lipid-enveloped structures.