Project description:The chromatin-based rules governing the selection and activation of replication origins remain to be elucidated. It is believed that DNA replication initiates from open chromatin domains, thus replication origins residing in regulatory elements that are located at open and active chromatin. However, we report here that lysine specific demethylase 1 (LSD1), which biochemically catalyzes H3K4me1/2 demethylation to favor chromatin condensation, interacts with the DNA replication machinery. We found that LSD1 level peaks in early S phase. We demonstrated that LSD1 promotes DNA replication by facilitating origin firing in euchromatic regions and through regulating replication timing. Indeed, euchromatic zones enriched in H3K4me2 are the preferred sites for pre-RC binding in early replication. Remarkably, LSD1 deficiency leads to a genome-wide switch from early to late in replication timing. We showed that LSD1-promoted DNA replication is mechanistically linked to the loading of TICRR (TopBP1-Interacting Checkpoint and Replication Regulator) onto the pre-RC and subsequent recruitment of the initiator Cdc45 during origin firing. Together, these results reveal an unexpected role for LSD1 in euchromatic origin firing and replication timing.
Project description:The chromatin-based rules governing the selection and activation of replication origins remain to be elucidated. It is believed that DNA replication initiates from open chromatin domains, thus replication origins residing in regulatory elements that are located at open and active chromatin. However, we report here that lysine specific demethylase 1 (LSD1), which biochemically catalyzes H3K4me1/2 demethylation to favor chromatin condensation, interacts with the DNA replication machinery. We found that LSD1 level peaks in early S phase. We demonstrated that LSD1 promotes DNA replication by facilitating origin firing in euchromatic regions and through regulating replication timing. Indeed, euchromatic zones enriched in H3K4me2 are the preferred sites for pre-RC binding in early replication. Remarkably, LSD1 deficiency leads to a genome-wide switch from early to late in replication timing. We showed that LSD1-promoted DNA replication is mechanistically linked to the loading of TICRR (TopBP1-Interacting Checkpoint and Replication Regulator) onto the pre-RC and subsequent recruitment of the initiator Cdc45 during origin firing. Together, these results reveal an unexpected role for LSD1 in euchromatic origin firing and replication timing.
Project description:The chromatin-based rules governing the selection and activation of replication origins remain to be elucidated. It is believed that DNA replication initiates from open chromatin domains, thus replication origins residing in regulatory elements that are located at open and active chromatin. However, we report here that lysine specific demethylase 1 (LSD1), which biochemically catalyzes H3K4me1/2 demethylation to favor chromatin condensation, interacts with the DNA replication machinery. We found that LSD1 level peaks in early S phase. We demonstrated that LSD1 promotes DNA replication by facilitating origin firing in euchromatic regions and through regulating replication timing. Indeed, euchromatic zones enriched in H3K4me2 are the preferred sites for pre-RC binding in early replication. Remarkably, LSD1 deficiency leads to a genome-wide switch from early to late in replication timing. We showed that LSD1-promoted DNA replication is mechanistically linked to the loading of TICRR (TopBP1-Interacting Checkpoint and Replication Regulator) onto the pre-RC and subsequent recruitment of the initiator Cdc45 during origin firing. Together, these results reveal an unexpected role for LSD1 in euchromatic origin firing and replication timing.
Project description:One of the long-standing questions in eukaryotic DNA replication is the mechanisms that determine where and when a particular segment of the genome is replicated. Cdc7/Hsk1 is a conserved kinase required for initiation of DNA replication, and may affect the site selection and timing of origin firing. We identified rif1∆, a null mutant of rif1+, a conserved telomere binding factor, as an efficient bypass mutant of fission yeast hsk1. Extensive deregulation of dormant origins over a wide range of the chromosomes occurs in rif1∆ in the presence or absence of HU. At the same time, many early-firing, efficient origins are suppressed or delayed in firing timing in rif1∆. Rif1 binds not only to telomeres but also to many specific locations on the arm segments that only partially overlap with the pre-Replicative Complex assembly sites, although Rif1 tends to bind in the vicinity of the late/ dormant origins activated in rif1∆. The binding to the arm segments occurs through M to G1 phase in a manner independent of Taz1 and appears to be essential for the replication timing program during normal cell cycle. Our data demonstrate that Rif1 is a critical determinant of origin activation program on the fission yeast chromosomes. BrdU incorporation profiles at early S-phase in Wild vs rif1∆. Cdc45 binding profiles at early S-phase in Wild vs rif1∆. Rif1 binidng sites aroud G1/S boudary and at M-phase. Mcm4 binding sites in wild, hsk1-89 temperature mutant and rif1∆.
Project description:The chromatin at origins of replication is thought to influence DNA replication initiation in eukaryotic genomes. However, it remains unclear how the chromatin composition controls the firing of early-efficient (EE) or late-inefficient (LI) origins. Here, we used site-specific recombination and single-locus chromatin isolation to purify EE and LI replication origins in Saccharomyces cerevisiae . Using mass spectrometry, we define the histone modification landscape and identify the protein composition of native chromatin regions surrounding the EE and LI replication start sites. In addition to the known origin interactors, we find novel origin-associated factors, such as the kinetochore-associated Ask1/DASH complex. Strikingly, we show that Ask1 regulates the replication timing control of specific origins in yeast. Thus, our unbiased approach identifies functionally-relevant proteomes at single-copy loci and would be widely applicable to provide an in-depth quantitative characterization of histone modification and protein interaction networks of chromatin at any genomic locus of interest.
Project description:How early- and late-firing origins are selected on eukaryotic chromosomes is largely unknown. Here we show that Mrc1, a conserved factor required for stabilization of stalled replication forks, selectively binds to the early-firing origins in a manner independent of Cdc45 and Hsk1 kinase in fission yeast. In mrc1∆ (and in swi1∆ to some extent), efficiency of firing is stimulated and its timing is advanced selectively at those origins that are normally bound by Mrc1. In contrast, the late or inefficient origins which are not bound by Mrc1 are not activated in mrc1∆. The enhanced firing and precocious Cdc45 loading at Mrc1-bound early-firing origins are not observed in a checkpoint mutant of mrc1, suggesting that non-checkpoint function is involved in maintaining the normal program of early-firing origins. We propose that pre-firing binding of Mrc1 is an important marker of early-firing origins which are precociously activated by the absence this protein. Mrc1 binding profiles at G1/S boundary or early S-phase in wild type vs hsk1-89 mutant.
Project description:We report the genome-wide mapping of Orc1 binding-sites in mammals and their validation as active DNA-replication origins (ORIs). Orc1 sites are universally associated with transcription start sites (TSSs) of coding or non-coding RNAs. Transcription levels at the Orc1 sites directly correlate with replication timing, suggesting the existence of two classes of ORIs: those associated with moderate/high transcription levels (M-bM-^IM-%1 RNA copy/cell), replicating in early S and mapping to the TSSs of coding RNAs, and those associated with low transcription levels (<1 RNA copy/cell), replicating throughout the entire S and mapping to TSSs of non-coding RNAs. These findings are compatible with a scenario whereby TSS expression-levels influence the efficiency of Orc1 recruitment at G1 and the probability of firing during S. Identification of Orc1 binding sites in human cells