title: Turnover of the major polypeptides of 40-S monomer particles.
abstract: The pulse-chase experiments with Friend erythroleukemia cells designed to reveal the metabolic properties of the protein complex of 40-S particles showed that the major polypeptides of this complex turn over with half-lives between 19 h and 206 h. the main conclusion from the experiments is that the complex does not degrade as a single unit. Since the individual polypeptides forming the complex live much longer than hnRNA, and in addition degrade at a different rate, we considered the following two modes of degradation as most likely. (1) The complex might not be subjected to a profound degradation at the end of the processing of associated pre-mRNA. In this case it should exist as a long-lived recyclable mosaic of metabolically differing polypeptides whose replacement takes place at a specific rate. (2) Alternatively, the protein complex might be completely degraded at the end of processing, but in a way that liberates free individual polypeptides available for recycling. The further experiments indicate that the 37 000-Mr, 34 000-Mr and 32 000-Mr core proteins in isolated 40-S particles and in particles associated with a nuclear fraction released from chromatin after micrococcal nuclease digestion degrade at different rates. These experiments suggest the existence of at least a metabolic heterogeneity among the population of nuclear particles carrying pre-mRNA.
mesh_terms: D000818:Animals; D003513:Cycloheximide / Q000494:pharmacology; D005622:Friend murine leukemia virus; D006207:Half-Life; D007942:Leukemia, Experimental / Q000378:metabolism; D051379:Mice; D008970:Molecular Weight; D009363:Neoplasm Proteins / Q000378:metabolism; D009698:Nucleoproteins / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism*; D012332:RNA, Heterogeneous Nuclear / Q000378:metabolism; D012334:RNA, Neoplasm / Q000378:metabolism; D012261:Ribonucleoproteins / Q000378:metabolism*
chemical_list: D009363:Neoplasm Proteins; D009698:Nucleoproteins; D010455:Peptides; D012332:RNA, Heterogeneous Nuclear; D012334:RNA, Neoplasm; D012261:Ribonucleoproteins; D003513:Cycloheximide