The cellular site of synthesis of ribosomal RNA in Tetrahymena pyriformis was studied by analyzing the purified nuclear and cytoplasmic RNA from cells pulse labeled with uridine-3H. The results of studies using zonal centrifugation in sucrose density gradients show that the ribosomal RNA is synthesized in the nucleus as a large precursor molecule sedimenting at 35S. The 35S molecule undergoes rapid transformation through two main nuclear intermediates, sedimenting at about 30S and 26S. The smaller ribosomal RNA (17S) appears first in the cytoplasm and it seems to be absent from the nucleus. The apparent delay in the appearance of the larger ribosomal RNA (26S) in the cytoplasm is due to the presence of a larger pool of its precursors in the nucleus as indicated by pulse-chase experiments. The newly synthesized ribosomal RNA's appear in the cytoplasm as discrete 60S and 45S ribonucleoprotein particles, before their incorporation into the polysomes.
Article| June 01 1970
RIBOSOME SYNTHESIS IN TETRAHYMENA PYRIFORMIS
From the Whitman Laboratory, Department of Biology, University of Chicago, Chicago, Illinois.
Dr. Kumar's present address is Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461
Received: March 11 1969
Revision Received: December 24 1969
Online Issn: 1540-8140
Print Issn: 0021-9525
Copyright © 1970 by The Rockefeller University Press
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Ajit Kumar; RIBOSOME SYNTHESIS IN TETRAHYMENA PYRIFORMIS . J Cell Biol 1 June 1970; 45 (3): 623–634. doi: https://doi.org/10.1083/jcb.45.3.623
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