Cell Nucleus Biogenesis, Structure and Function
Nuclear basket ring
: See Vasu, S.K., Forbes, D.J. (2001) Nuclear
pores and nuclear assembly,
Curr. Opin. Cell Biol.
, 363–375 ±or ±urther details.
dimensions of 120
80 nm. This com-
plex has a striking eightfold symmetry
as well as providing the structure of
the channel between the nucleus and
cytoplasm, which serves to fuse the in-
ner and outer nuclear membranes. The
eight spokes of the channel are held
together to form a major scaffold of
2. These spokes surround a central trans-
porter complex that is
60-nm high and
40 nm in diameter.
3. The cytoplasmic face of the pore com-
plex has 8 cytoplasmic Flaments that
extend about 50 nm into the cytoplasm.
4. The nucleoplasmic face of the pore has
8 Flaments of 100 to 150 nm that extend
into the nucleus. In some situations,
these appear to associate at their distal
end to generate a basket-like structure
at the nuclear face of the pore complex.
Nuclear pores are the gateways between
the nuclear and cytoplasmic compart-
ments. Small molecules are able to pass
through the pores by simple diffusion.
Studies on diffusion kinetics suggest that
a cylindrical diffusion channel of
exists between the pore spokes and the
central transporter complex. Proteins or
RNA–protein complexes that are
and smaller are able to pass through this
diffusion channel, but larger complexes
are not and must rely on active trans-
The components of the vertebrate pore
complex and their probable location in
active transport, the critical steps involve
the initial interaction of the nuclear trans-
port complex – that is, the cargo – with
the pore Flaments that extend into either
teins are involved in active transport as
The Nuclear Lamina
During the 1960s, it was recognized that
nuclei from mammalian cells had a pro-
tein network between the nuclear envelope
and peripheral chromatin. This network
or lamina is composed of a branched
network of polymerized lamin proteins.