In eukaryotic cells genome is confined within membrane-enclosed cell nucleus requiring intense macromolecular communication across the nuclear border. It is estimated that every minute around 1kg of material crosses nuclear membrane in all cells in our body. This traffic occurs through 100 nm channels embedded into the nuclear membrane, the Nuclear Pore Complexes (NPC). The are ~ 2000-4000 of them in the human cell nucleus and ~ 100-200 in yeast.
The NPCs are among the most elaborate protein complexes in eukaryotic cells. Each structure is~ 100 MDa in size and consists of 500-1000 protein molecules - nucleoporins. There are around 30 different kinds of nucleoporins, each with own functional profile. The largest class, scaffold nucleoporins, form NPC walls and another big class - Phenyalanine-Glycine (FG) repeat nucleoporins - fill up the NPC transport channel. The FG segments are natively unfolded and work to prevent free NPC passage of any reasonably large macromolecules (>40 kDa), except for special Nuclear Transport Receptors (NTRs) that mediate nucleoytoplamic transport.
The interactions between NTRs, FG repeats, transported molecules and various regulatory factors establish nucleocytoplamic communication - the major NPC function. The NPCs have also other important roles in the cell including chromatin organisation, regulation of gene expression, DNA replication/repair or cell differentiation. Recently the NPC attracted a lot of attention being implicated in pathogenesis of many ageing-related disorders.
It is intriguing how new NPCs assemble. To make a new NPC cells must somehow produce a fusion pore in the membrane and to insert the multi-magadalton complex into it without perturbing the diffusion barrier by yet unclear mechanism. This is particularly non-trivial task in cells with the intact nuclear membrane like human neurones and could be the reason for accumulating NPC defects in the ageing brain. We are focusing on understanding the mechanisms of de novo NPC assembly using budding yeast, which is an extremely powerful genetic and biochemical model system. Although yeast is a unicellular organism, the yeast NPCs always stay in the intact nuclear membrane, keeping many parallels with the NPCs in cell types like human brain cells.