SUMM4 complex biochemically couples insulator function and DNA replication timing control

Abstract

AbstractThe mechanisms that establish DNA replication timing programs in eukaryotes remain incompletely understood. Drosophila SNF2-related factor SUUR imparts under-replication (UR) of late-replicating intercalary heterochromatin (IH) in polytene chromosomes. We developed a proteomics technique termed MERCI to isolate a native complex SUMM4 comprising SUUR and chromatin boundary protein Mod(Mdg4)-67.2. Mod(Mdg4) stimulates the ATPase activity of SUUR and is required for its normal spatiotemporal distribution in vivo. Both SUMM4 subunits mediate the activities of gypsy insulator disrupting enhancer-promoter interactions and establishing chromatin barriers. Furthermore, SuUR or mod(mdg4) mutations reverse UR of IH. Our findings uncover a critical role for architectural proteins in attenuating replication fork progression and suggest an alternative mechanism for DNA replication timing that does not depend on an asynchronous firing of replication origins.One-Sentence SummaryA stable protein complex comprising an insulator factor and a SNF2-like ATPase imparts late replication of heterochromatin.