The amino-terminal domain of the lamin B receptor is a nuclear envelope targeting signal

The rim-staining fluorescence patterns seen for transfected cells expressing LBR and the LBR-chicken hepatic lectin chimeric protein are consistent with a location in the inner nuclear membrane, but could also be seen if these proteins were localized to the nuclear pore membranes or to the outer nuclear membrane. To further confirm an inner nuclear membrane localization of these polypeptides, their accessibility to antibodies was determined in unfixed digitoninpermeabilized cells. Treatment of cultured cells with appropriate amounts of digitonin removes the plasma membrane but leaves the nuclear envelope intact (Adam et al., 1990) .