AN INTEGRAL MEMBRANE-PROTEIN OF THE PORE MEMBRANE DOMAIN OF THE NUCLEAR-ENVELOPE CONTAINS A NUCLEOPORIN-LIKE REGION

We have identified an integral membrane protein of 145 kD (estimated b y SDS-PAGE) of rat liver nuclear envelopes that binds to WGA. We obtai ned peptide sequence from purified p145 and cloned and sequenced sever al cDNA clones and one genomic clone. The relative molecular mass of p 145 calculated from its complete, cDNA deduced primary structure is 12 0.7 kD. Antibodies raised against a synthetic peptide represented in p 145 reacted monospecifically with p145. In indirect immunofluorescence these antibodies gave punctate staining of the nuclear envelope. Immu nogold EM showed specific decoration of the nuclear pores. Thus p145 i s an integral membrane protein located specifically in the ''pore memb rane'' domain of the nuclear envelope. To indicate this specific locat ion, and based on its calculated relative molecular mass, the protein is termed POM 121 (pore membrane protein of 121 kD). The 1,199-residue -long primary structure shows a hydrophobic region (residues 29-72) th at is likely to form one (or two adjacent) transmembrane segment(s). T he bulk of the protein (residues 73-1199) is predicted to be exposed n ot on the cisternal side but on the pore side of the pore membrane. It contains 36 consensus sites for various kinases. However, its most st riking feature is a repetitive pentapeptide motif XFXFG that has also been shown to occur in several nucleoporins. This nucleoporin-like dom ain of POM 121 is proposed to function in anchoring components of the nuclear pore complex to the pore membrane.