title: Subunit association defects in Escherichia coli ribosome mutants lacking proteins S20 and L11.
abstract: The subunit association capacity of 30S and 50S ribosomal subunits from Escherichia coli mutants lacking protein S20 or L11 as well as of 50S subunits depleted of L7/L12 was tested by sucrose gradient centrifugation and by a nitrocellulose filtration method based on the protection from hydrolysis with peptidyl-tRNA hydrolase of ribosome-bound AcPhe-tRNA. It was found that the subunits lacking either S20 or L11 display an altered association capacity, while the 50S subunits lacking L7/L12 have normal association behavior. The association of S20-lacking 30S subunits is quantitatively reduced, especially at low Mg2+ concentrations (5-12 mM), and produces loosely interacting particles which dissociate during sucrose gradient centrifugation. The association of L11-lacking 50S subunits is quantitatively near-normal at all Mg2+ concentrations and produces loosely associating particles only at low Mg2+ concentrations (5-8 mM); the mechanism of their association with 30S subunits, however, or the structure of the resulting 30S-50S couples is altered in such a way as to cause the ejection of an AcPhe-tRNA molecule pre-bound to the 30S subunits in response to poly(U).
authors.affiliation: Max-Planck-Institut für Molekulare Genetik, Abteilung Wittmann, Berlin-Dahlem.
authors.forename: F
authors.initials: F
authors.lastname: Götz
authors.forename: C
authors.initials: C
authors.lastname: Fleischer
authors.forename: C L
authors.initials: CL
authors.lastname: Pon
authors.forename: C O
authors.initials: CO
authors.lastname: Gualerzi
mesh_terms: D001426:Bacterial Proteins / Q000032:analysis / Q000235:genetics* / Q000502:physiology; D001665:Binding Sites / Q000187:drug effects; D002499:Centrifugation, Density Gradient; D004926:Escherichia coli / Q000032:analysis / Q000235:genetics*; D006868:Hydrolysis; D008274:Magnesium / Q000494:pharmacology; D009154:Mutation; D011485:Protein Binding; D012343:RNA, Transfer / Q000032:analysis; D012269:Ribosomal Proteins / Q000032:analysis / Q000235:genetics* / Q000502:physiology; D012270:Ribosomes / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D012269:Ribosomal Proteins; C027624:ribosomal protein L11; C029611:ribosomal protein S20; C040469:ribosomal protein S30; C016700:ribosomal protein L7-L12; D012343:RNA, Transfer; D008274:Magnesium