title: Polyribosome size analysis. Measurement of number-average polyribosome sizes.
abstract: The analysis of translational efficiencies of specific mRNAs requires a determination of the polyribosome size. The appropriate value to use in such calculations is the number-average size. A method is described for accurately measuring the number-average size of total and of specific protein synthesizing polyribosomes using isokinetic sucrose density gradients and 125I-labeled antibodies. By this method, we demonstrated that albumin synthesizing polyribosomes from a serum albumin secreting mouse hepatoma cell line exist over a broad range from trimers to 20-mers (mean 6-10). The specificity of antibody interaction with polyribosomes was demonstrated using cells not synthesizing mouse serum albumin, and by demonstrating that 125I-anti ovalbumin does not bind to mouse hepatoma polyribosomes. Treatment of the mouse hepatoma cells with 1 MUM cycloheximide shifted practically all of the monomers into polyribosomes resulting in an increase in the number-average size of the albumin synthesizing polyribosomes. Cycloheximide treatment, however, did not eliminate the size heterogeneity in the albumin synthesizing polyribosomes.
mesh_terms: D000418:Albumins / Q000096:biosynthesis; D000818:Animals; D000918:Antibody Specificity; D002460:Cell Line; D002499:Centrifugation, Density Gradient; D003513:Cycloheximide / Q000494:pharmacology; D006801:Humans; D051379:Mice; D010316:Particle Size; D011132:Polyribosomes / Q000187:drug effects / Q000276:immunology / Q000648:ultrastructure*; D014176:Protein Biosynthesis; D012313:RNA
chemical_list: D000418:Albumins; D012313:RNA; D003513:Cycloheximide