The first membrane spanning region of the lamin B receptor is sufficient for sorting to the inner nuclear membrane

Next we made a chimeric construct (Ru-p58) in which the nucleoplasmic domain, up to residue 190, was replaced by the small subunit of RuBPCase, a protein that is located in chloroplasts. Immunolocalization showed nuclear rim staining characteristic of LBR (Fig. 5 B) . These data indicated that substitution of the nucleoplasmic domain by a heterologous protein still yields sorting to the inner nuclear membrane. These data suggest that the nucleoplasmic domain is not required for sorting to the inner nuclear membrane. Figure 6 . The first transmembrane region of LBR sorts/3-galactosidase to the inner nuclear membrane. (A) COS-1 cells transfected with/3gal-TM1 (B) were fixed and permeabilized 24 h after transfection and processed for indirect immunofluorescence microscopy by staining with mouse anti-/3-galactosidase antibodies, followed by anti-mouse IgG-FITC. (B) shows the amino acid sequence encoded by the chick p58 sequence contained in the/3gal-TM1 construct. The stippled box encloses the predicted membrane spanning segment. Bar, 10 #m.