Transport across the nuclear pore complex is an essential process for regulating cell growth and normal development. The structure of the nuclear pore and its involvement in nuclear transport are being studied at a molecular level. Previously the laboratory has shown that the nuclear pore complex is made up of a family of glycoproteins having covalently attached O-linked N-acetylglucosamine. Glycosylation of the major nuclear pore glycoprotein p62 has been examined in detail. The rat cDNA and gene encoding rat p62 have been isolated. Examination of the primary sequence of p62 revealed a series of 14 repeating pentapeptide motifs having the sequence GFSFG. Rabbit antisera raised against this pentapeptide sequence react not only with p62 but also with the other members of the nuclear pore glycoprotein family. These antisera have been used to isolate the cDNAs encoding other nuclear pore glycoproteins. In addition, degenerate oligonucleotides corresponding to the pentapeptide repeat have been used as primers for isolating additional cDNA species using the polymerase chain reaction technique. To examine the function of the nuclear pore glycoproteins in nuclear transport, an in vitro nuclear assembly and transport system has been employed. When DNA is added to extracts of Xenopus laevis nuclei reform with intact nuclei envelopes and nuclear pores. These extracts can be depleted of endogenous nuclear pore components and reconstituted with recombinant or biochemically altered pore proteins. Using this assay nuclear pore assembly and transport were shown to require nuclear pore glycoproteins; the O-linked N-acetylglucosamine moiety can be modified without altering transport. The ability to generate recombinant forms of other nuclear pore glycoproteins should allow a further dissection of the functional roles of these nuclear pore components.
