SUMMARY PR-Set7/Set8 is a cell cycle-regulated enzyme that monomethylates lysine 20 of histone H4 (H4K20). Set8 and monomethylated H4K20 are virtually undetectable during G1 and S phases of the cell cycle but increase in late S and in G2. We identify CRL4Cdt2 as the principal E3 ubiquitin ligase responsible for Set8 proteolytic degradation in the S-phase of the cell cycle, which requires Set8-PCNA interaction. Inactivation of the CRL4-Cdt2-PCNA-Set8 degradation axis results in (a) DNA damage and the induction of tumor suppressor p53 and p53-transactivated pro-apoptotic genes, (b) delayed progression through G2 phase of the cell cycle due to activation of the G2/M check-point, (c) specific repression of histone gene transcription and depletion of the histone proteins, and (d) repression of E2F1-dependent gene transcription. These results demonstrate a central role of CRL4Cdt2-dependent cell cycle regulation of Set8 for the maintenance of a stable epigenetic state essential for cell viability.

The MCM2-7 helicase complex is loaded on DNA replication origins during the G1 phase of the cell cycle to license the origins for replication in S phase. How the initiator primase-polymerase complex, DNA polymerase ␣ (pol ␣), is brought to the origins is still unclear. We show that And-1/Ctf4 (Chromosome transmission fidelity 4) interacts with Mcm10, which associates with MCM2-7, and with the p180 subunit of DNA pol ␣. And-1 is essential for DNA synthesis and the stability of p180 in mammalian cells. In Xenopus egg extracts And-1 is loaded on the chromatin after Mcm10, concurrently with DNA pol ␣, and is required for efficient DNA synthesis. Mcm10 is required for chromatin loading of And-1 and an antibody that disrupts the Mcm10-And-1 interaction interferes with the loading of And-1 and of pol ␣, inhibiting DNA synthesis. And-1/Ctf4 is therefore a new replication initiation factor that brings together the MCM2-7 helicase and the DNA pol ␣-primase complex, analogous to the linker between helicase and primase or helicase and polymerase that is seen in the bacterial replication machinery. The discovery also adds to the connection between replication initiation and sister chromatid cohesion.[Keywords: And-1/CTF4; DNA replication; genome stability; cell cycle; DNA polymerase] Supplemental material is available at http://www.genesdev.org.

Summary RVB1/RVB2 are two highly conserved members of the AAA+ family that are present in different protein and nucleoprotein complexes. Recent studies implicate that RVB-containing complexes play a role in variable cellular processes such as transcription, DNA damage response, snoRNP assembly, cellular transformation and cancer metastasis. In this review we discuss recent advances in the understanding of RVB-containing complexes and the functions of RVBs in these pathways.

The Rvb1p and Rvb2p (or TIP48 and TIP49) nuclear ATP binding proteins are universally conserved in eukaryotes and essential for viability of yeasts. Rvbp associate with each other as a double hexamer, with YHR034c and with two complexes involved in chromatin remodeling, Ino80.com and Swr1.com. Loss of Rvb1p or Ino80p affects many yeast promoters similarly. Rvbp are not essential for the recruitment of Ino80p to promoters but are essential for the catalytic activity of Ino80.com. Loss of Rvbp leads to loss of the functionally critical Arp5p in Ino80.com. Rvb2p associates with Arp5p in vitro in a reaction dependent on the presence of ATP and Ino80p. Therefore, Rvbp are required for the structural and functional integrity of the Ino80 chromatin remodeling complex.