Oligomers of the ATPase EHD2 confine caveolae to the plasma membrane through association with actinCaveolae are plasma membrane microdomains that play important roles in signalling and endocytosis. The ATPase EHD2 shuttles on and off the static population of caveolae in an ATPase cycledependent manner and links caveolae to actin filaments confining them to the plasma membrane.

Dbf4-dependent kinase (DDK) and cyclin-dependent kinase (CDK) are essential to initiate DNA replication at individual origins. During replication stress, the S-phase checkpoint inhibits the DDK-and CDK-dependent activation of late replication origins. Rad53 kinase is a central effector of the replication checkpoint and both binds to and phosphorylates Dbf4 to prevent late-origin firing. The molecular basis for the Rad53-Dbf4 physical interaction is not clear but occurs through the Dbf4 N terminus. Here we found that both Rad53 FHA1 and FHA2 domains, which specifically recognize phospho-threonine (pT), interacted with Dbf4 through an N-terminal sequence and an adjacent BRCT domain. Purified Rad53 FHA1 domain (but not FHA2) bound to a pT Dbf4 peptide in vitro, suggesting a possible phospho-threonine-dependent interaction between FHA1 and Dbf4. The Dbf4-Rad53 interaction is governed by multiple contacts that are separable from the Cdc5-and Msa1-binding sites in the Dbf4 N terminus. Importantly, abrogation of the Rad53-Dbf4 physical interaction blocked Dbf4 phosphorylation and allowed late-origin firing during replication checkpoint activation. This indicated that Rad53 must stably bind to Dbf4 to regulate its activity.T HE fidelity of chromosome replication depends on checkpoint mechanisms to stabilize stalled forks, regulate origin activation, and repair DNA damage (Hartwell and Weinert 1989;Bartek et al. 2004;Segurado and Tercero 2009). In response to replication stress, the replication checkpoint maintains replisome stability and prevents late origins from firing, which allows time for DNA repair and the completion of DNA replication prior to chromosome segregation. Incomplete DNA replication or uncoordinated origin firing following DNA damage can result in genomic instability, cancer predisposition, and premature aging (Branzei and Foiani 2010).In the budding yeast Saccharomyces cerevisiae, activation of the checkpoint sensor kinase Mec1 (vertebrate ATR, Ataxia Telangiectasia and Rad3-related) is triggered at stalled forks or sites of DNA damage (Majka et al. 2006;Labib and De Piccoli 2011). Subsequent signal amplification through the Mrc1 or Rad9 adaptors leads to activation of the checkpoint kinase Rad53 (the ortholog of the human tumor suppressor Chk2) (Branzei and Foiani 2009). Rad53 is an integral transducer of various cellular responses to replication stress or DNA damage. Rad53 induces a series of transcriptional responses through MBF-regulated genes (Bastos de Oliveira et al. 2012;Travesa et al. 2012) and also activates the Dun1 kinase, which promotes the expression of ribonucleotide reductase (RNR) subunits and additional DNA repair genes (Huang et al. 1998). In parallel, Rad53 down-regulates the RNR inhibitor Sml1 to increase deoxyribonucleotide levels and facilitate DNA synthesis (Zhao et al. 2001). In response to replication fork stalling, Rad53 prevents the activation of late replication origins by phosphorylating two proteins required for the initiation of DNA replication: Dbf4 and Sld3 (...

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