title: The ribosomes of Drosophila. Normal and defective ribosome biosynthesis in Drosophila cell cultures.
abstract: The assembly of proteins and RNA into mature ribosomal subunits has been studied in Drosophila cell cultures by pulse-chase experiments. Pulse labeled rRNA has a transit time of 3 h, while the transfer of ribosomal protein occurs completely within 30 min. Inhibition of protein synthesis by cycloheximide results in an almost immediate cessation of ribosome assembly, a result which indicates that no large pool of free ribosomal proteins exists in the cell. Substituting pre-ribosomal RNA with the analogue 5-fluorouridine (5-FU) results in a cessation of ribosome muturation. Under these conditions at least three large subunit proteins continue to accumulate on pre-existing cytoplasmic subunits, indicating an exchange. A portion of ribosomal subunit proteins synthesized in the presence of 5-FU can be recovered in cytoplasmic subunits once the effect of 5-FU has been reversed. This is most easily interpreted in terms of their stabilization on substituted pre-rRNA within the nucleolus, and subsequent utilization on unsubstituted RNA.
mesh_terms: D000241:Adenosine / Q000378:metabolism; D002460:Cell Line; D002466:Cell Nucleolus / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D004330:Drosophila; D005472:Fluorouracil / Q000494:pharmacology*; D066298:In Vitro Techniques; D012335:RNA, Ribosomal / Q000096:biosynthesis*; D012269:Ribosomal Proteins / Q000096:biosynthesis*; D012270:Ribosomes / Q000378:metabolism*; D014529:Uridine / Q000378:metabolism
chemical_list: D012335:RNA, Ribosomal; D012269:Ribosomal Proteins; D003513:Cycloheximide; D000241:Adenosine; D005472:Fluorouracil; D014529:Uridine