PROTEIN KINESIS - NUCLEOCYTOPLASMIC TRANSPORT

Active transport of proteins and RNAs between the nucleus and cytoplas m is a major process in eukaryotic cells. Recently, factors that recog nize transport substrates and mediate nuclear import or export have be en characterized, revealing interactions that target substrates to the nuclear pore complexes, through which translocation occurs. Transloca tion requires energy, and for the import process this energy is at lea st partly consumed by the action of the small guanosine triphosphatase Ran. In the first half of the review, some of the well-established ge neral background information on nucleocytoplasmic transport is discuss ed. The second half describes recent information on the mechanistic de tails of nuclear import and export as well as major unresolved issues such as how directionality is conferred on either import or export. Th e whole review is slanted toward discussion of metazoan cells.