Fig 1.

Striking parallels between the transition from proliferation and quiescence in budding yeast and metazoans In dividing yeast and metazoan cells, transcription factor complexes of Swi4 and Swi6 (or SBF) and E2F1, 2, or 3 and DP1 activate a set of genes that promote the transition to S phase. Whi5 and RB or RB-like (RBL) pocket proteins (p107 and p130) inhibit these complexes in G1, until Cyclin/Cdk kinases phosphorylate (P) and release them from the DNA binding complexes and allow transcription to procede. When cells exit the cell cycle, there are quiescence-specific complexes that form on these promoters to maintain a stable, but reversible G1 arrest. In metazoans, different quiescence-specific E2F and RB-like proteins bind. In yeast, there is no evidence of substitutes for Swi4 and Swi6. In these repressed complexes of both yeast and metazoans, additional proteins are recruited, including the highly conserved histone deacetylase complex of Rpd3(HDAC1)/Sin3/Sds3, which deactylates histones and represses transcription. These quiescence-specific complexes also include Msa1 and Msa2 in yeast and the MuvB complex in worms, flies and humans.