Lamin B constitutes an intermediate filament attachment site at the nuclear envelope

We found that urea extraction of turkey erythrocyte nuclear envelopes abolished their ability to bind exogenous 125I-vimentin, while, at the same time, it removed the nuclear lamins from the membranes. After purification of the lamins from such urea extracts, a specific binding between isolated vimentin and lamin B, or a lamin A + B hetero- oligomer, was detected by affinity chromatography. Similar analysis revealed that the 6.6-kD vimentin tail piece was involved in this interaction. By other approaches (quantitative immunoprecipitation, rate zonal sedimentation, turbidometric assays) a substoichiometric lamin B-vimentin binding was determined under in vitro conditions. It was also observed that anti-lamin B antibodies but not other sera (anti- lamin A, anti-ankyrin, preimmune) were able to block 70% of the binding of 125I-vimentin to native, vimentin-depleted, nuclear envelopes. These data, which were confirmed by using rat liver nuclear lamins, indicate that intermediate filaments may be anchored directly to the nuclear lamina, providing a continuous network connecting the plasma membrane skeleton with the karyoskeleton of eukaryotic cells.