The bidirectional nucleocytoplasmic transport of macromolecules is mediated by the nuclear pore complex (NPC) which, in yeast, is composed of approximately 30 different proteins (nucleoporins). Pre-embedding immunogold-electron microscopy revealed that Nic96p, an essential yeast nucleoporin, is located about the cytoplasmic and the nuclear periphery of the central channel, and near or at the di...

Human immunodeficiency virus type 1 (HIV-1) commandeers host cell proteins and machineries for its replication. Our earlier work showed that HIV-1 induced the cytoplasmic retention of nucleocytoplasmic shuttling and ribonucleic acid (RNA)-binding proteins. This retention is dependent on nuclear export of the viral genomic RNA and on changes in the localization and expression level of the nucleo...

The nuclear envelope mediates nucleocytoplasmic communication. Nuclear pores transport proteins and RNA into and out of the nucleus. The pore is believed to allow free ion diffusion. Using an electrophysiological approach, we show the possible semipermeable properties of the envelope. To accomplish these functions we hypothesize a mechanism in which the pore complex acts as a molecular diaphragm.

In this issue, Frey and Görlich (2007) provide new insight into the selective barrier that controls protein traffic through the nuclear pore complex. They show that a single protein domain of the nuclear pore protein Nsp1 can form a hydrogel that allows highly selective access of nuclear transport receptors and their cargos, but rejects other proteins of similar size.

Many cargoes destined for nuclear import carry nuclear localization signals that are recognized by karyopherins (Kaps). We present methods to quantitate import rates and measure Kap and cargo concentrations in single yeast cells in vivo, providing new insights into import kinetics. By systematically manipulating the amounts, types, and affinities of Kaps and cargos, we show that import rates in...

The nuclear pore complex (NPC) is the gatekeeper of the nucleus, capable of actively discriminating between the active and inert cargo while accommodating a high rate of translocations. The biophysical mechanisms underlying transport, however, remain unclear due to the lack of information about biophysical factors playing role in transport. Based on published experimental data, we have establis...

Revealing the behavior of single molecules in living cells is very useful for understanding cellular events. Quantum dot probes are particularly promising tools for revealing how biological events occur at the single molecule level both in vitro and in vivo. In this review, we will introduce how single quantum dot applications are used for single molecule tracking. We will discuss how single qu...

To understand the cell, we need to determine the macromolecular assembly structures, which may consist of tens to hundreds of components. First, we review the varied experimental data that characterize the assemblies at several levels of resolution. We then describe computational methods for generating the structures using these data. To maximize completeness, resolution, accuracy, precision, a...

Covalent attachment of ubiquitin to target proteins, or ubiquitylation, has emerged as one of the most prevalent posttranslational modifications (PTMs), regulating nearly every cellular pathway. The diversity of functions associated with this particular PTM stems from the myriad ways in which a target protein can be modified by ubiquitin, e.g., monoubiquitin, multi-monoubiquitin, and polyubiqui...

CAN/Nup214, an essential component of the vertebrate nuclear pore complex (NPC), is required for proper cell cycle progression and nucleocytoplasmic transport. It is a member of the FG-repeat-containing family of nucleoporins and has been localized to the cytoplasmic face of the NPC. Indirect immunofluorescence studies with specific antibodies have shown that moderate overexpression of human CA...