title: Thermal down-regulation of exportable rRNA in nuclei.
abstract: The export of rRNP particles from nuclei isolated from Tetrahymena was investigated after preincubating the nuclei at different temperatures under nonpermissive export-conditions. We observed a new phenomenon: Temperature elevation from the sublethal cells' growth temperature, 8 degrees C, to the optimal temperature, 28 degrees C, lead to a gradual down-regulation in the maximal proportion of rRNP particles subsequently exported from nuclei at 28 degrees C. This thermal down-regulation is apparently not due to qualitative changes in the exported rRNP particles, a derangement in the gross nuclear organization, a degradation and/or nicking of the nuclear rRNA, a gross decomposition of the major nuclear proteins, a random cross-linking of nuclear components by disulfide bonds, or an elution of nuclear factors possibly required for rRNP export. Moreover, there is a corresponding thermal down-regulation in nuclear envelope-free nuclei. Our data indicate that nuclei possess a mechanism that regulates the number of potentially exportable rRNP particles at a level preceding the rRNP passage through the nuclear envelope.
mesh_terms: D000818:Animals; D001692:Biological Transport; D002467:Cell Nucleus / Q000502:physiology*; D006358:Hot Temperature; D007700:Kinetics; D008854:Microscopy, Electron; D009685:Nuclear Envelope / Q000502:physiology; D012335:RNA, Ribosomal / Q000378:metabolism*; D012261:Ribonucleoproteins / Q000378:metabolism; D012269:Ribosomal Proteins / Q000378:metabolism; D013769:Tetrahymena pyriformis / Q000378:metabolism*
chemical_list: D012335:RNA, Ribosomal; D012261:Ribonucleoproteins; D012269:Ribosomal Proteins