Open AccessNascent Subribosomal Particles in Tetrahymena pyriformis
Author(s) -
Leick Vagn,
Engberg Jan,
Emmersen Julius
Publication year - 1970
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1970.tb00923.x
Subject(s) - tetrahymena pyriformis , ribosomal rna , ribosome , ribosomal protein , tetrahymena , moiety , amino acid , protein biosynthesis , chemistry , phosphate , biochemistry , rna , crystallography , biophysics , biology , stereochemistry , gene
The metabolism and physical‐chemical properties of nascent (precursor) 40 and 60 S subribosomal particles have been studied in exponentially growing Tetrahymena pyriformis GL. Analysis of formaldehyde‐fixed 40 and 60 S particles in isopycnic CsCl gradients reveals that they have a lower buoyant density than the corresponding 30 and 50 S ribosomal sub‐units. Moreover, overall labeling of the cells with [ 3 H]amino acid and [ 32 P]phosphate shows that the precursor particles attain larger 3 H/ 32 P ratios than the corresponding sub‐units, indicating that the precursor particles contain extra (accessory) protein that splits off when they are converted into ribosomal sub‐units. The extra protein constitutes 10 to 20% of the total structural protein. Experiments in pulse‐labeling with radioactive amino acids indicate that 40 and 60 S particles are very rapidly labeled. This suggests that, apart from the RNA moiety, at least part of the structural ribosomal protein moiety associated with the nascent particles is newly synthesized. The possible involvement of 40 and 60 S particles in sub‐unit exchange between rounds of translation was investigated by comparing their kinetics of labeling with that of the ribosomal sub‐units. The results of the comparison indicate that the rate of recycling of ribosomal sub‐units through the pool of 40 and 60 S particles is too slow to account for sub‐unit exchange between each round of translation.