Purification and characterisation of p99, a nuclear modulator of protein phosphatase 1 activity

FEBS Lett. 1997 Dec 22;420(1):57-62. doi: 10.1016/s0014-5793(97)01485-3.


We have purified a form of protein phosphatase 1 (PP1) from HeLa cell nuclei, in which the phosphatase is complexed to a regulatory subunit termed p99. We report here the cloning and characterisation of the p99 component. p99 mRNA is widely expressed in human tissues and immunofluorescence analysis with anti-p99 antibodies showed a punctate nucleoplasmic staining with additional accumulations within the nucleolus. The C-terminus of p99 contains seven RGG RNA-binding motifs, followed by eleven decapeptide repeats containing six or more of the following conserved residues (GHRPHEGPGG), and finally a putative zinc finger domain. Recombinant p99 suppresses the phosphorylase phosphatase activity of PP1 by > 90% and the canonical PP1-binding motif on p99 (residues 396-401) is unusual in that the phenylalanine residue is replaced by tryptophan.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Cell Extracts
  • Cell Nucleolus / chemistry
  • Cell Nucleus / chemistry
  • Conserved Sequence
  • DNA-Binding Proteins
  • Gene Expression
  • HeLa Cells
  • Humans
  • Molecular Sequence Data
  • Molecular Weight
  • Nuclear Proteins / genetics
  • Nuclear Proteins / isolation & purification*
  • Nuclear Proteins / metabolism*
  • Organ Specificity
  • Phosphoprotein Phosphatases / metabolism*
  • Protein Binding
  • Protein Phosphatase 1
  • RNA, Messenger / analysis
  • RNA-Binding Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Zinc Fingers


  • Cell Extracts
  • DNA-Binding Proteins
  • Nuclear Proteins
  • PPP1R10 protein, human
  • RNA, Messenger
  • RNA-Binding Proteins
  • Recombinant Fusion Proteins
  • Phosphoprotein Phosphatases
  • Protein Phosphatase 1