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Nuclear genes determine structure and function in eukaryotes.
activity is regulated by extra- and intracellular
signals which travel from cytosolic to
Most of them use the
nuclear pore complexes (NPCs) (at the nuclear envelope, NE, see
Laskey, 1998) which regulate the transported cargo
(transcription factors, mRNA, etc.) .
Since 1990, patch-clamp (e.g.,
Matzke et al., 1990;
Mazzanti et al., 1990)
has confirmed classical microelectrode experiments (see refs. below) supporting the idea that NPCs also regulate ion fluxes (reviewed in
Loewenstein et al., 1966).
NPC ion channel behavior is viewed under the macromolecule-conducting ion channel paradigm (
Bustamante et al., 1995a, see below).
These experiments validate patch-clamp as a method for the assessment of
nuclear signaling and, thus for the understanding of the mechanisms of control of gene activity and expression..
Thus, they are of relevance to
On the right is shown the NPC model from Aebi's group in Basel. The figure is taken from Panté & Aebi, 1994 (with permission). The putative central plug or transporter, containing the famed p62 complexes, is drawn in fuzzy color to indicate the controversy on whether it forms part of the NPC (see below). Cytoplasmic filaments are represented by the vertical, rod-like structures. Nucleoplasmic filaments, on the other side, converge to form basket-like structures. The plug is recognized as an electron-dense material under EM. The material is less frequently seen when macromolecular transport substrates are added. This suggests that the plug is not part of the NPC but material in transit caught during specimen fixation (thus the fuzzy color in the figure). With some exceptions, NPC plugging and macromolecular transport seems to depend on Ca2+(see below) and on RanGTP (see illustrations from the Max Planck Society and The Scientist). Recent advances in proteomics has uncovered the complexities of NPC gating (e.g., Rout & Aitchison, 2001 - full paper with excellent pictures).
NPC Ion Channel Behavior & The Molecular Coulter Counter Concept
We are investigating NPC structure and function with
confocal, atomic force microscopy (AFM) and,
transmission and field-emission electron microscopies (TEM and FESEM).
Our results demonstrate that due to their poor electrical charge carrier properties, macromolecules (e.g., transcription factors and DNAs, RNAs) and other particles reduce NPC channel conductance (e.g.,
Bustamante et al., 1995a).
This macromolecule-conducting channel paradigm (see animation below) has been recently applied to the measurement of nucleic acids (e.g.,
Kasianowicz et al., 1996;
Hanss et al., 1998;
Akeson et al., 1999;
Lubensky & Nelson, 1999;
Meller et al., 1999).
macromolecular size increases, the pore becomes plugged and there is no ion flow.
This effect is analogous to that of cells in a Coulter counter (e.g.,
Bezrukov et al., 1994 ;
Bezrukov & Kasianowicz, 1997;
Merzlyak et al., 1999).
For a review on the molecular Coulter counter, see
Fig 2 of
Daneholt (1997) illustrates an RNP particle (high molecular weight RNA associated with proteins) being exported (with permission).
The study by
Kiseleva et al. (1998) with field emission SEM demonstrates the interactions between mRNA and NPCs.
Our paradigm is shown below (see
Bustamante et al., 1995a).
Note that plugging of the NPC diffusional channel was proposed on the basis of fluorescence microscopy observations (see page 350 of Reiner Peters' review
Peters, 1986; see also
Keminer & Peters, 1999).
Mitochondrial ion channels show plugging similar to what we believe is the plugging of NPC ion channel activity (press here for some references on mitochondrial channel).
Endoplasmic reticulum (ER) ribosomal channels also showed channel plugging by proteins (see
Simon et al., 1989;
Simon & Blobel, 1991,
1992). Finally, plant thylakoid membrane channels stop ion flow during protein translocation (e.g.
Teter & Theg, 1998).
Selected References (the pros and cons)
|NPC By AFM|
Our Publications In Nuclear Physiology
2002 2001a, b 2000a, b 1998 1996 1995a, b, c 1994a, b, c 1993a 1992a
Get Some of The Latest Information on Signal Transduction
Attend On- or Off-Line NIH Videocast Conferences
Nobel Prizes in Physiology and Medicine (Lectures, Symposia, etc.)
Click on the links above for the full lists.
Click on the link below for a selected list.
Selected Nobel Prize Lectures, Symposia, etc.
Marine Biological Lab Conferences
NIH Video-Symposium: Insights from the DNA Sequence of the Human Genome (February 12, 2001).
With Words From Watson And Crick
NIH Video-Conference: First Analysis of Complete Human Genome Press (February 12, 20001)
Nature Genomics Gateway
Front cover reprinted by permission from Nature 409: Feb 15, 2001 copyright 2001 Macmillan Magazines Ltd.
Science's Feb 16, 2001
First Plant Genome
(contact us if we missed yours)
|Transport Mechanisms from Dani Stoffler's Site|
|List of Scientists Working in This and Related Fields|
Schematics Of Patch-Clamp Setup
Check out the Axon Instruments Patch-Clamp Instrumentation and Theory (The Axon Guide).
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