THE LAMIN-B RECEPTOR-ASSOCIATED PROTEIN-P34 SHARES SEQUENCE HOMOLOGY AND ANTIGENIC DETERMINANTS WITH THE SPLICING FACTOR-2-ASSOCIATED PROTEIN-P-32

The lamin B receptor (p58) is an inner nuclear membrane protein that f orms an in vivo complex with the nuclear lamins, a nuclear envelope ki nase, and two other nuclear proteins with apparent M(r) of 18,000 (pig ) and 34,000 (p34). We now report the isolation of p34 by partial diss ociation of the immunoaffinity-purified p58 protein complex. Determina tion of the N-terminal amino acid sequence of purified p34 shows that this polypeptide is homologous to p32, a splicing factor 2 (SF2)-assoc iated protein. The relatedness between p34 and p32 can be further esta blished by showing that antibodies raised against N- and C-terminal pe ptides of p32 doss-react with purified p34. As the amino acid sequence of p58 contains an arginine/serine (RS)-rich region similar to the RS -rich region found in SF 2, we speculate that these domains provide bi nding sites for p34 and that this protein may be a linker between the nuclear membrane and intranuclear spliceosomal substructures.