title: Maturation of ribosomes in yeast. I Kinetic analysis by labelling of high molecular weight rRNA species.
abstract: To study the maturation of ribosomes in Saccharomyces carlsbergensis, protoplasts were pulse labeled with [5-3H]uridine at 15 degrees C. Investigation of the cellular location of pulse-labelled ribosomal RNA precursor and mature ribosomal RNA shows that both the 37-S precursor RNA, common to both 17-S and 26-S rRNA, as well as the 29-S RNA, the direct precursor of 26-S rRNA, are located in the nucleus. Most of the 18-S RNA, the direct precursor of 17-S rRNA, is found in the cytoplasmic fraction. Apart from 37-S and 29-S RNA the nucleus also contains an appreciable amount of 26-S rRNA as well as a small quantity of 18-S RNA. These data indicate that processing of 29-S to 26-S RNA occurs in the nucleus, whereas the conversion of 18-S RNA to 17-S rRNA takes place in the cytoplasm. The kinetics of appearance of pulse-labelled 26-S and 17-S rRNA in the various cytoplasmic ribosomal particles indicate, that newly formed 40-S ribosomal particles are almost immediately incorporated into 80-S ribosomes and polysomes. On the other hand, there appears to exist a fairly large cytoplasmic pool of newly synthesized ribosomal particles containing 26-S rRNA and sedimenting at about 60 S. The kinetics of appearance of newly formed 26-S and 17-S rRNA in mature ribosomes show that the maturation of the large ribosomal subunit takes about twice as much time as that of the small subunit.
mesh_terms: D002458:Cell Fractionation; D002467:Cell Nucleus / Q000378:metabolism*; D002499:Centrifugation, Density Gradient; D003593:Cytoplasm / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D008956:Models, Chemical; D008970:Molecular Weight; D011132:Polyribosomes / Q000378:metabolism; D011523:Protoplasts / Q000378:metabolism; D012335:RNA, Ribosomal / Q000096:biosynthesis*; D012261:Ribonucleoproteins / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism* / Q000648:ultrastructure; D012440:Saccharomyces / Q000378:metabolism* / Q000648:ultrastructure; D014529:Uridine / Q000378:metabolism
chemical_list: D046911:Macromolecular Substances; D012335:RNA, Ribosomal; D012261:Ribonucleoproteins; D014529:Uridine