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Hi Don

I am interested in your pdf about compartmentalization behaviors of fluorophores.  Thanks in advance.

Monique Vasseur
Microscopie et imagerie
Département de biochimie
Université de Montréal
C.P. 6128, succursale Centre-ville
Montréal QC    H3C 3J7   Canada
tél. (514) 343-6111 poste 5148
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-----Message d'origine-----
De : Confocal Microscopy List [mailto:[log in to unmask]] De la part de Donald M. O'Malley
Envoyé : 19 mars 2007 13:58
À : [log in to unmask]
Objet : "brighter" GFP and other molecules in the nucleus

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Hi Folks,

Anything smaller than about 70,000 MW can freely
enter and exit the nucleus, it seems.  [targeting
sequences notwithstanding]

Since the nuclear interior is "all nucleoplasm" while
the cytoplasm is only about 50% cytosol, the apparent
lower "concentration" of molecules within the cytoplasm
is thus (often) about half of that in the nucleus, which
can be explained by such hydrophilic molecules being
largely excluded by cytoplasmic organelles and thus
confined to the  "aqueous space" of the cell: i.e. the cytosol
plus the contiguous nucleoplasm.

Ideally, if one could image cytoplasm at high enough
resolution to resolve small organelles and the intervening
cytosol, one should be able to see that molecules like
GFP and fluorescent dextrans have high concentrations
in the cytosol and are excluded from small membrane
bound organelles.  In such cases, their **cytosolic**
concentration should be about the same as their
nucleoplasmic concentration.

Of course, this is only a first approximation, since most fluorophores
seem to have their own unique personality, with different
binding and compartmentalization behaviors.  But the
volume exclusion effect should apply to all hydrophilic
molecules, as discussed further in a 1994 PDF of mine--
available free of charge!

FYI,
Don

Donald M. O'Malley
Associate Professor
Dept. Biology
Northeastern University