The Journal of Cell Biology, Vol 87, 589-593, Copyright © 1980 by The Rockefeller University Press
Mechanism for the selection of nuclear polypeptides in Xenopus oocytes. II. Two-dimensional gel analysis
CM Feldherr and JA Ogburn
The role of the nuclear envelope in controlling intracellular protein
exchanges was investigated in vivo, by determining the effect of altering
nuclear permeability on (a) the protein composition of the nucleoplasm and
(b) the nuclear uptake rates of specific endogenous proteins. The nuclear
envelopes were disrupted by puncturing oocytes in the region of the
germinal vesicle by use of glass needles. Nuclear proteins were analyzed in
punctured and control cells by two- dimensional gel electrophoresis,
fluorography, and double-labeling techniques. Over 300 nuclear polypeptides
were identified in the fluorographs. Of this number, only approximately
10-15 were found to vary between punctured and control nuclei; furthermore,
different polypeptides varied in each experiment. These qualitative studies
indicate that specific binding within the nucleoplasm, and not selection by
the envelope, is the main factor in maintaining the protein composition of
the nucleus. The nuclear uptake rates of five individual polypeptides,
ranging in molecular weight from 43,000 to 100,000, were analyzed by use of
double-labeling procedures. Only one of the polypeptides (actin) entered
the nuclei more rapidly after disruption of the envelope. That the nuclear
uptake of certain endogenous proteins is unaffected by puncturing
demonstrates that passage across the envelope is not a rate-limiting step
in the nucleocytoplasmic exchange of these molecules.
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