THE NUCLEAR-PORE COMPLEX PROTEIN P62 IS ONE OF SEVERAL SIALIC ACID-CONTAINING PROTEINS OF THE NUCLEAR-ENVELOPE

While investigating the glycosylation of nuclear envelope proteins of neuroblastoma cells, we found several proteins that bound the sialic a cid-specific Sambucus nigra agglutinin, The strongest signals were obt ained for proteins with apparent molecular masses of 66 and 180 kDa, T he specificity of the lectin binding was checked by acylneuraminyl hyd rolase treatment of nuclear envelope proteins, which prohibited S. nig ra agglutinin binding, Digestion of nuclear envelope proteins with the N-glycosidase F revealed that sialic acid was N-glycosidically linked to the 180-kDa protein and very probably O-glycosidically linked to t he 66-kDa protein, Upon extraction, the latter behaved like the nucleo porin p62 in that it was partly extracted by high ionic strength buffe rs, could not be solubilized by nonionic detergent, and was completely removed from the nuclear envelope with urea, Two-dimensional gel elec trophoretic comparison showed that the S. nigra agglutinin-binding pro tein and p62 have an identical isoelectric point of about 5.0 and an i dentical apparent molecular mass of 66 kDa, This, together with the bi nding of the anti-nucleoporin antibody, demonstrated the identity of t he 66-kDa sialoprotein and p62, S. nigra agglutinin inhibits nuclear p rotein transport in neuroblastoma cells, strongly suggesting a functio nal significance of sialylation of p62.