title: Kinetic analysis of fraction I protein biosynthesis in young protoplasts of tobacco leaves.
abstract: At maximum inhibition chloramphenicol reduced [35S] methionine incorporation into acid-insoluble materials of sterile protoplasts from young tobacco leaves 5-7 cm in length by 30% compared to 70% by cycloheximide, indicating that 30% of the [35S] methionine became incorporated into chloroplast proteins and 70% into cytoplasmic proteins. [35S] Methionine became incorporated into both the large and small subunits of Fraction I protein, the major soluble protein of chloroplasts. Rifampicin and streptolydigin inhibited [3H] uridine incorporation into the 23 and 16 S rRNAs of chloroplasts to a much greater extent than into the 25 and 18 S cytoplasmic rRNAs. Rifampicin inhibited [35S] metionine incorporation into Fraction I protein after the third hour of incubation; streptolydigin after 2 h, the former evidently preventing initiation of mRNA for the large subunit of Fraction I protein and the latter its elongation. About 2.5 h was required between initiation of the large subunit mRNA synthesis, and appearance of the protein. It was estimated that 45 min is required for transcription of the mRNA which has a half-life of 2 h and that 105 min is required for its translation into approximately 350 amino acids constituting the large subunit monomeric polypeptide. The effect of chloramphenicol, cycloheximide and 2-(4-methyl-2,6-dinitroanaline)-N-methyl propionamide, the latter an inhibitor of protein initiation by 80 S ribosomes, on kinetics of Fraction I protein synthesis indicate that protoplasts contain a pool of small subunit polypeptides and that 30 min is required to polymerize the approximately 100 amino acids constituting the primary structure.
mesh_terms: D000617:Aminoglycosides; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002701:Chloramphenicol / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D007700:Kinetics; D008854:Microscopy, Electron; D010940:Plant Proteins / Q000096:biosynthesis*; D010944:Plants; D010947:Plants, Toxic; D014176:Protein Biosynthesis / Q000187:drug effects; D011523:Protoplasts / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D012293:Rifampin / Q000494:pharmacology; D014026:Nicotiana
chemical_list: D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D010940:Plant Proteins; D002701:Chloramphenicol; D003513:Cycloheximide; D012293:Rifampin