Rats were given radioactive L-leucine intravenously. At various times after injection, the livers were removed and separated into nuclear and cytoplasmic fractions by a nonaqueous technique. Glyceraldehyde-3-phosphate dehydrogenase, aldolase, and lactic dehydrogenase were isolated from each cell fraction by antibody precipitation followed by gel electrophoresis, and the specific radioactivities of the isolated enzymes were determined. In all three cases, the onset of labeling and the rate of incorporation were the same for the nuclear enzyme as for the corresponding enzyme from the cytoplasm. If we assume that equilibration of the enzymes between the cytoplasmic and nuclear pools occurs slowly relative to the labeling times employed, we may conclude that the labeled nuclear enzymes either were synthesized in the nucleus or moved into the nucleus from a cytoplasmic site of synthesis without first passing into the cytoplasmic pool of enzyme. Treatment with puromycin, an antibiotic which depresses incorporation into cytoplasmic proteins to a greater extent than into nuclear proteins, led to a situation in which the specific activities of the nuclear enzymes were several times as high as those of the corresponding cytoplasmic enzymes following a short period of incorporation. These data substantiate the assumption that equilibration between the cytoplasmic and nuclear enzyme pools occurs slowly and provide further evidence that the labeled nuclear enzymes do not arise from the cytoplasmic enzyme pool.
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1 July 1971
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July 01 1971
STUDIES ON THE SITE OF SYNTHESIS OF SEVERAL SOLUBLE ENZYMES OF THE CELL NUCLEUS
LeRoy Kuehl,
LeRoy Kuehl
From the Department of Biochemistry, University of Utah, Salt Lake City, Utah 84112
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Earl N. Sumsion
Earl N. Sumsion
From the Department of Biochemistry, University of Utah, Salt Lake City, Utah 84112
Search for other works by this author on:
LeRoy Kuehl
From the Department of Biochemistry, University of Utah, Salt Lake City, Utah 84112
Earl N. Sumsion
From the Department of Biochemistry, University of Utah, Salt Lake City, Utah 84112
Received:
August 20 1970
Revision Received:
November 17 1970
Online ISSN: 1540-8140
Print ISSN: 0021-9525
Copyright © 1971 by The Rockefeller University Press
1971
J Cell Biol (1971) 50 (1): 1–9.
Article history
Received:
August 20 1970
Revision Received:
November 17 1970
Citation
LeRoy Kuehl, Earl N. Sumsion; STUDIES ON THE SITE OF SYNTHESIS OF SEVERAL SOLUBLE ENZYMES OF THE CELL NUCLEUS . J Cell Biol 1 July 1971; 50 (1): 1–9. doi: https://doi.org/10.1083/jcb.50.1.1
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