Restricting conformational flexibility of the switch II region creates a dominant-inhibitory phenotype in Obg GTPase Nog1

Mol Cell Biol. 2007 Nov;27(21):7735-44. doi: 10.1128/MCB.01161-07. Epub 2007 Sep 4.

Abstract

Nog1 is a conserved eukaryotic GTPase of the Obg family involved in the biogenesis of 60S ribosomal subunits. Here we report the unique dominant-inhibitory properties of a point mutation in the switch II region of mouse Nog1; this mutation is predicted to restrict conformational mobility of the GTP-binding domain. We show that although the mutation does not significantly affect GTP binding, ectopic expression of the mutant in mouse cells disrupts productive assembly of pre-60S subunits and arrests cell proliferation. The mutant impairs processing of multiple pre-rRNA intermediates, resulting in the degradation of the newly synthesized 5.8S/28S rRNA precursors. Sedimentation analysis of nucleolar preribosomes indicates that defective Nog1 function inhibits the conversion of 32S pre-rRNA-containing complexes to a smaller form, resulting in a drastic accumulation of enlarged pre-60S particles in the nucleolus. These results suggest that conformational changes in the switch II element of Nog1 have a critical importance for the dissociation of preribosome-bound factors during intranucleolar maturation and thereby strongly influence the overall efficiency of the assembly process.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cell Nucleolus / metabolism
  • Centrifugation, Density Gradient
  • GTP Phosphohydrolases / chemistry*
  • GTP Phosphohydrolases / metabolism*
  • Guanosine Triphosphate / metabolism
  • Kinetics
  • Mice
  • Molecular Sequence Data
  • Nucleic Acid Hybridization
  • Phenotype
  • Point Mutation / genetics
  • Protein Structure, Tertiary
  • RNA Precursors / metabolism
  • RNA Processing, Post-Transcriptional
  • Ribosomes / metabolism
  • Structure-Activity Relationship

Substances

  • RNA Precursors
  • Guanosine Triphosphate
  • GTP Phosphohydrolases
  • Nog1 protein, mouse