Regulation of the Chlamydomonas cell cycle by a stable, chromatin-associated retinoblastoma tumor suppressor complex

Plant Cell. 2010 Oct;22(10):3331-47. doi: 10.1105/tpc.110.076067. Epub 2010 Oct 26.


We examined the cell cycle dynamics of the retinoblastoma (RB) protein complex in the unicellular alga Chlamydomonas reinhardtii that has single homologs for each subunit-RB, E2F, and DP. We found that Chlamydomonas RB (encoded by MAT3) is a cell cycle-regulated phosphoprotein, that E2F1-DP1 can bind to a consensus E2F site, and that all three proteins interact in vivo to form a complex that can be quantitatively immunopurified. Yeast two-hybrid assays revealed the formation of a ternary complex between MAT3, DP1, and E2F1 that requires a C-terminal motif in E2F1 analogous to the RB binding domain of plant and animal E2Fs. We examined the abundance of MAT3/RB and E2F1-DP1 in highly synchronous cultures and found that they are synthesized and remain stably associated throughout the cell cycle with no detectable fraction of free E2F1-DP1. Consistent with their stable association, MAT3/RB and DP1 are constitutively nuclear, and MAT3/RB does not require DP1-E2F1 for nuclear localization. In the nucleus, MAT3/RB remains bound to chromatin throughout the cell cycle, and its chromatin binding is mediated through E2F1-DP1. Together, our data show that E2F-DP complexes can regulate the cell cycle without dissociation of their RB-related subunit and that other changes may be sufficient to convert RB-E2F-DP from a cell cycle repressor to an activator.

Publication types

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

MeSH terms

  • Cell Cycle*
  • Chlamydomonas / cytology*
  • Chlamydomonas / genetics
  • Chlamydomonas / metabolism
  • Chromatin / metabolism*
  • E2F Transcription Factors / genetics
  • E2F Transcription Factors / metabolism
  • Gene Expression Regulation, Plant
  • Molecular Sequence Data
  • Phosphoproteins / genetics
  • Phosphoproteins / metabolism
  • Phosphorylation
  • Plant Proteins / metabolism*
  • Protozoan Proteins / genetics
  • Protozoan Proteins / metabolism*
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Retinoblastoma Protein / genetics
  • Retinoblastoma Protein / metabolism*
  • Transcription Factor DP1 / genetics
  • Transcription Factor DP1 / metabolism
  • Two-Hybrid System Techniques


  • Chromatin
  • E2F Transcription Factors
  • Phosphoproteins
  • Plant Proteins
  • Protozoan Proteins
  • Recombinant Proteins
  • Retinoblastoma Protein
  • Transcription Factor DP1
  • mat3 protein, Chlamydomonas

Associated data

  • GENBANK/AAK68064
  • GENBANK/AAV41810
  • GENBANK/AAV68604
  • GENBANK/DQ417491
  • GENBANK/DQ417492
  • GENBANK/GU784915
  • GENBANK/U54830
  • RefSeq/NP_566417
  • RefSeq/XP_002948442
  • RefSeq/XP_002955099