title: Rate-limiting factors for lymphocyte protein synthesis. Ribosome commitment and the capacity of lymphocyte cell-free systems to translate exogenous mRNAs.
abstract: The properties of the protein synthesising systems of different lymphocyte preparations have been compared with those of non-lymphoid tissues. Polysome profiles from rat thymocytes, sheep mesenteric lymphocytes, rat liver and mouse ascites tumours showed that the commitment of ribosomes to protein synthesis in lymphocytes was relatively low. Initiation factor activities, assessed on the abilities of post-mitochondrial fractions to support exogenous mRNA translation, were limited or undetectable in lymphoid tissues. While the thymocyte system translated globin mRNA, the response was enhanced by ascites extracts rich in initiation factors. The mesenteric lymphocyte system responded only marginally to globin mRNA and poly(U) but the responses were not enhanced by ascites extracts. The activity of isolated  mesenteric ribosomes was comparable with ribosomes from other tissues, indicating that extraribosomal factors were responsible for the poor overall activity of the mesenteric system. Finally, the effects of cycloheximide on the recruitment of polysomes in lymphocytes indicated that the commitment of ribosomes to protein synthesis might be restricted by both limited mRNA availability and limited capacity for initiation of mRNA translation.
mesh_terms: D000818:Animals; D001798:Blood Proteins / Q000096:biosynthesis*; D007700:Kinetics; D008214:Lymphocytes / Q000378:metabolism*; D008297:Male; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D012270:Ribosomes / Q000378:metabolism*; D012756:Sheep; D013950:Thymus Gland / Q000378:metabolism
chemical_list: D001798:Blood Proteins; D012333:RNA, Messenger