The rules and roles of nucleocytoplasmic shuttling proteins

The spatial separation of mRNA synthesis from translation, while providing eukaryotes with the possibility to achieve higher complexity through a more elaborate regulation of gene expression, has set the need for transport me chanisms through the nuclear envelope. In a simplistic view of nucleocytopl asmic transport, nuclear proteins are imported into the nucleus while RNAs are exported to the cytoplasm, The reality is, howe,er, that transport of e ither proteins or RNAs across the nuclear envelope can be bi-directional, D uring the past years, an increasing number of proteins have been identified that shuttle continuously back and forth between the nucleus and the cytop lasm, The emerging picture is that shuttling proteins are key factors in co nveying information on nuclear and cytoplasmic activities within the cell, (C) 2001 Federation of European Biochemical Societies, Published by Elsevie r Science B.V. All rights reserved.