Title : Partial cDNA sequence encoding a nuclear pore protein modified by O-linked N-acetylglucosamine.
Abstract :
The nuclear pore complex contains a family of proteins ranging in molecular mass from 35 to 220 kDa that are glycosylated with O-linked N-acetylglucosamine (GlcNAc) residues.
We sought to determine the primary sequence of a nuclear pore protein modified by O-linked GlcNAc.
The major (62 kDa) nuclear pore glycoprotein ( np62 ) was purified from rat liver nuclear envelopes by immunoaffinity chromatography and preparative gel electrophoresis
After CNBr fragmentation , a glycopeptide was isolated and microsequenced
An oligonucleotide probe based on this sequence information was used to screen a lambda gt11 cDNA library constructed from poly(A) mRNA of the rat thyroid cell line FRTL-5
A clone (B5) was isolated and shown to hybridize to a single 2.5-kilobase species in poly(A) mRNA from rat liver and FRTL-5
This insert was sequenced and found to contain a 691-base-pair cDNA encoding a 155-amino acid open reading frame
This open reading frame contained a CNBr fragment identical to the original glycopeptide sequence and a second CNBr fragment corresponding to a nonglycosylated peptide that was also isolated from the purified pore glycoprotein
The B5 cDNA produced a beta-galactosidase fusion protein of the size predicted by the open reading frame
Analysis of the residues making up a presumptive glycosylation site suggests that the sequence is unlike any known sites for enzymatic N- or O-linked glycosylation
The partial sequence of the 62-kDa nuclear pore glycoprotein shows little similarity to other characterized proteins and elucidates structural features of a member of the family of nuclear pore glycoproteins