Cell Nucleus Biogenesis, Structure and Function
393
Tab. 3
Vertebrate nucleoporins.
Nucleoporin
Likely location
FG
repeats?
vNup153
Nuclear basket ring
FG
vNup50
Nuclear basket
FG
vNup98
Nuclear basket
GLFG
vGle2 (Rae1)
vNup160
Nuclear side
vNup133
Nuclear side
vNup107
Nuclear side
vNup96
Nuclear side
sec13
vNup155
Both sides
vNup188
Spokes/nuclear
vNup205
Spokes/nuclear
vNup93
Spokes/nuclear
vNup62
Central transporter
FG
vNup58
Central transporter
FG
vNup54
Central transporter
FG
vNup45
Central transporter
FG
vPOM121
Integral membrane
FG
vgp210
Integral membrane
vNup88 (84)
Cytoplasmic flaments
vNup214
(CAN)
Cytoplasmic flaments
FG
vGle1
Cytoplasmic flaments
vNup358
(RanBP2)
Cytoplasmic flaments
FG
RanBP1
Cytoplasmic flaments
hCG1
Cytoplasmic flaments
Note
: See Vasu, S.K., Forbes, D.J. (2001) Nuclear
pores and nuclear assembly,
Curr. Opin. Cell Biol.
13
, 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
the pore.
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.
3.1.1
Pore Function
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
9nm
exists between the pore spokes and the
central transporter complex. Proteins or
RNA–protein complexes that are
50 kDa
and smaller are able to pass through this
diffusion channel, but larger complexes
are not and must rely on active trans-
port systems.
The components of the vertebrate pore
complex and their probable location in
thecomplexareshowninTable3.During
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
thenuc
leuso
rcy
top
lasm
.Thepo
rep
ro
-
teins are involved in active transport as
described below.
3.2
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.
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