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

Bradley J.S.C. Olson, Michael Oberholzer, Yubing Li, James M. Zones, Harjivan S. Kohli, Katerina Bisova, Su Chiung Fang, Jill Meisenhelder, Tony Hunter, James G. Umena

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60 Scopus citations

Abstract

We examined the cell cycle dynamics of the retinoblastoma (RB) protein complex in the unicellular alga 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 phosphorprotein, that E2F1-DP1 can bind to a consensus E2F site, and that all three proteins interact in vivo to form 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.

Original languageEnglish
Pages (from-to)3331-3347
Number of pages17
JournalPlant Cell
Volume22
Issue number10
DOIs
StatePublished - Oct 2010

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