Mitosis-specific phosphorylation of gar2, a fission yeast nucleolar protein structurally related to nucleolin

Chromosoma. 1997 Jun;105(7-8):532-41. doi: 10.1007/BF02510490.

Abstract

The nucleolar protein gar2 of fission yeast is structurally related to the multifunctional nucleolar protein nucleolin from vertebrates and has been shown to be implicated in production of 18S rRNA. gar2 contains several potential casein kinase 2 (CK2) phosphorylation sites and a single putative p34(cdc2 )phosphorylation site in the consensus S50PKK. Here, we show that, like nucleolin, gar2 is phosphorylated in vitro by both highly purified CK2 from CHO cells and p34(cdc2 )from starfish oocytes. Moreover, the substitution of alanine for the N-terminal serine 50 abolishes phosphorylation by p34(cdc2 )in vitro. We also provide evidence that gar2 is phosphorylated in vitro by a p13(suc1)-Sepharose-bound kinase from Schizosaccharomyces pombe extracts that displays cell cycle-regulated activity similar to that of the p34(cdc2(kinase. In vivo 32P labeling of cells indicates that gar2 is a phosphoprotein and that incorporation of phosphate on residue 50 occurs specifically at mitosis. Taken together, these results lead us to propose that gar2 is likely to be an in vivo substrate for the mitotic p34(cdc2 )kinase. However, this posttranslational modification of the gar2 protein does not appear to be essential for normal production of 18S rRNA.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alanine / genetics
  • Alanine / metabolism
  • Animals
  • Binding Sites
  • CDC2 Protein Kinase / genetics
  • CDC2 Protein Kinase / metabolism
  • CHO Cells / enzymology
  • Casein Kinase II
  • Cell Cycle / physiology
  • Cell Nucleolus / chemistry
  • Cell Nucleolus / metabolism
  • Cricetinae
  • Cyclin-Dependent Kinases / genetics
  • Cyclin-Dependent Kinases / metabolism
  • Female
  • Fungal Proteins / chemistry
  • Fungal Proteins / genetics*
  • Fungal Proteins / metabolism*
  • Mitosis*
  • Mutation
  • Nuclear Proteins / chemistry*
  • Nuclear Proteins / genetics*
  • Nuclear Proteins / metabolism*
  • Oocytes / enzymology
  • Phosphoproteins / chemistry*
  • Phosphoproteins / metabolism
  • Phosphorylation
  • Protein Processing, Post-Translational
  • Protein-Serine-Threonine Kinases / metabolism
  • RNA, Ribosomal, 18S / genetics
  • RNA, Ribosomal, 18S / metabolism
  • RNA-Binding Proteins*
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Schizosaccharomyces / enzymology
  • Schizosaccharomyces / genetics*
  • Schizosaccharomyces pombe Proteins*
  • Serine / metabolism
  • Starfish
  • Temperature

Substances

  • Fungal Proteins
  • GAR2 protein, S pombe
  • Nuclear Proteins
  • Phosphoproteins
  • RNA, Ribosomal, 18S
  • RNA-Binding Proteins
  • Recombinant Proteins
  • Schizosaccharomyces pombe Proteins
  • nucleolin
  • Serine
  • Casein Kinase II
  • Protein-Serine-Threonine Kinases
  • CDC2 Protein Kinase
  • Cyclin-Dependent Kinases
  • Alanine