All NPCs appear to function both in nuclear import and export. NPCs are thus unique amongst cellular transporters in their large size (-300 times the mass of a gap junction), variety of substrates and number of functions. One might expect this diversity of roles to be reflected in the diversity and number of NPC components; it has been estimated that there may be upwards of 50 distinct polypeptides comprising the NPC. A variety of biochemical, immunological, and genetic approaches have been employed to isolate NPC proteins. We are currently employing our newly developed mass spectrometric protein identification tools (i.e., our MALDI-ITMS instrument together with the program """"""""Pepfrag"""""""" as well as MALDI-TOF-MS with the program """"""""Profound"""""""" to accelerate the identification of as yet unidentified nuclear pore proteins. It is our aim to identify them all. We have analyzed more than 350 protein bonds from SDS-PAGE gel fractions of enriched yeast nuclear pore complex preparations. At present, we are testing the various open reading frames that we have identified to ascertain whether any of them are new nucleoporins (or nuclear pore related proteins).
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