Identification of specific polypeptides of the nuclear envelope by iodination of mouse liver nuclei

A sensitive technique is described for the rapid identification of nuclear-envelope proteins. Mouse liver nuclei (purified on sucrose gradients) were iodinated with Na125I by the immobilized water-insoluble reagent Iodogen. Iodinated nuclei were digested with RNAase A and DNAase I and then salt-extracted to obtain labelled nuclear envelopes. Nuclear envelopes were characterized by morphological and biochemical criteria and by SDS/polyacrylamide-gel electrophoresis. In all, 13 polypeptides of molecular masses 145, 115, 98, 85, 75, 70, 65, 54, 50, 45, 40, 38 and 36 kDa were identified in the labelled nuclear envelopes. The labelled polypeptides were localized to the nuclear envelope by extraction of the envelope with Triton X-100 and different concentrations of salt. Iodination of intact nuclei was shown to be specific for the nuclear envelope by the absence of labelling of histones and cytoplasmic contaminants.