Project description:To characterize the binding sites of RBMX and RPA on chromatin, 293T cells were treated with CPT and binding profiles were obtained by ChIP-seq assay. RBMX ChIP-seq profile was highly correlated with RPA ChIP-seq profile, both showing strong peaks at centromeres. To characterize the occupancy sites bound by both RBMX and RPA, we annotated their shared peaks. The results showed that these sequences are mostly enriched on repetitive DNAs including rRNA, simple repeats and satellite DNAs.
Project description:Ongoing CAG expansions in Spinocerebellar ataxia type 1 (SCA1) and Huntington disease (HD) brains exacerbate disease. Expansions involve aberrant repair of mutagenic slipped-DNAs, formed from single-stranded DNAs. Whether singlestranded DNA-binding proteins prevent or facilitate expansions is unknown. We assessed canonical RPA (RPA1-RPA2-RPA3) and Alternative-RPA (RPA1-RPA4- RPA3), containing primate-specific RPA4. RPA is essential for all DNA metabolism. Alt-RPA has undefined functions. Alt-RPA is upregulated 10-fold in HD and SCA1 patient brains. RPA enhances, while Alt-RPA blocks, correct repair of slipped-CAGs. RPA, but not Alt-RPA, efficiently binds and melts slipped-DNAs. RPA enhances, while Alt-RPA blocks, removal of excess slipped-DNAs by FAN1 nuclease. Protein-protein interactomes reveal unique and shared partners of RPA and Alt-RPA, including expansion-driving proteins. RPA-overexpression in SCA1 mice inhibits CAG expansions in brains, rescuing neuron morphology and motor phenotypes. Modulating repeat mutations is one example involving antagonistic Alt-RPA↔RPA interactions, illuminating questions as to which RPA-mediated processes are also modulated by AltRPA.
Project description:Single-stranded DNA (ssDNA) binding protein Replication Protein A (RPA) is essential for protecting ssDNA at replication forks. However, how RPA is loaded to replication forks remains unexplored. Here, we show that Regulator of Ty1 transposition protein 105 (Rtt105) binds RPA and is required for the association of RPA with replication forks. Cells lacking Rtt105 exhibit dramatic genome instability and severe defects in DNA replication. Intriguingly, both the RPA nuclear import and its ability to bind DNA replication forks were greatly compromised in rtt105 mutant cells, however, targeting RPA to the nucleus cannot rescue the defect of RPA binding to replication forks. Importantly, Rtt105 promotes the binding of RPA to ssDNA but does not associate with the final RPA-ssDNA complex in vitro. Moreover, single-molecule studies revealed that Rtt105 affects the binding mode of RPA to ssDNA. These results support a model in which Rtt105 functions as an RPA chaperone that escorts RPA to nucleus and assemble RPA onto ssDNA at replication forks.
Project description:Chromatin replication requires tight coordination of nucleosome assembly machinery with DNA replication machinery. While significant progress has been made in characterizing histone chaperones in this process, the mechanism of whereby nucleosome assembly couples with DNA replication remains largely unknown. Here we show that replication protein A (RPA), a single-stranded DNA (ssDNA) binding protein that is essential for DNA replication provides a binding platform for H3-H4 deposition by histone chaperons and is required for nucleosome formation on nascent chromatin. RPA binds free histone H3-H4 but not nucleosomal histones, and a RPA coated ssDNA stimulates assembly of H3-H4 onto double strand DNA in vitro. RPA mutant with reduced H3-H4 binding exhibits synthetic genetic interaction with mutations at key factors involved in replication-coupled (RC) nucleosome assembly, and are defective in assembly of replicating DNA into nucleosomes in cells. These results reveal a novel function for RPA in nucleosome assembly and a mechanism whereby nucleosome assembly is coordinated with DNA replication.
Project description:Single-stranded DNA (ssDNA) binding protein Replication Protein A (RPA) is essential for protecting ssDNA at replication forks. However, how RPA is guided to DNA replication forks remains unclear. Here, we show that Regulator of Ty1 transposition protein 105 (Rtt105) is an RPA-binding protein and is required for the binding of RPA at replication forks. Cells lacking Rtt105 exhibit extensive genome instability and severe defects in DNA replication. Both the nuclear import of RPA and the extent of genome-wide binding of RPA at replication forks were greatly compromised in rtt105 mutant cells. Mechanistically, Rtt105 is required for the interaction of RPA with Kap95, an importin protein known to be essential for RPA’s nuclear import. Remarkably, Rtt105 strongly enhances RPA binding with ssDNA substrates in vitro. We therefore propose a model in which Rtt105 functions as a RPA chaperone that both escorts RPA during nuclear important and delivers RPA to replication forks.
Project description:Single stranded DNA binding proteins play many roles in nucleic acid metabolism, but their importance during transcription remains unclear. Quantitative proteomic analysis of RNA polymerase II (RNApII) pre-initiation complexes (PICs) identified Sub1 and the Replication Protein A complex (RPA), both of which bind single-stranded DNA (ssDNA). Sub1, homolog of mammalian coactivator PC4, exhibits strong genetic interactions with factors necessary for promoter melting. Sub1 localizes near the transcription bubble in vitro and binds to promoters in vivo dependent upon PIC assembly. In contrast, RPA localizes to transcribed regions of active genes, strongly correlated with transcribing RNApII but independently of replication. RFA1 interacts genetically with transcription elongation factor genes. Interestingly, RPA levels increase at active promoters in cells carrying a Sub1 deletion or ssDNA binding mutant, suggesting competition for a common binding site. We propose that Sub1 and RPA interact with the non-template strand of RNApII complexes during initiation and elongation, respectively. Chip-chip from wt and sub1D cells with Rfa1 Chromatin immunoprecipitation (ChIP) of Rfa1 in wt and sub1D yeast demonstrated that Rfa1 localization correlates with RNA Polymerase II and is increased at some transcription start sites when Sub1 has been deleted. Comparison of Rfa1 localization in wt vs sub1D yeast
Project description:AID promotes chromosomal translocations by inducing DNA double-strand breaks (DSBs) at immunoglobulin (Ig) genes and oncogenes in G1. RPA is a ssDNA-binding protein that associates with resected DSBs in the S phase and facilitates the assembly of factors involved in homologous repair (HR) such as Rad51. Notably, RPA deposition also marks sites of AID-mediated damage, but its role in Ig gene recombination remains unclear. Here we demonstrate that RPA associates asymmetrically with resected ssDNA in response to lesions created by AID, RAG, or other nucleases. Small amounts of RPA are deposited at AID targets in G1 in an ATM-dependent manner. In contrast, recruitment in S-G2/M is extensive, ATM-independent, and associated with Rad51 accumulation. RPA in S-G2/M increases in NHEJ-deficient lymphocytes, where there is more extensive DNA-end resection. Thus, most RPA recruitment during CSR represents salvage of un-repaired breaks by homology-based pathways during the S-G2/M phases of the cell cycle. Chip-Seq of RPA from mouse activated B cells (n = 40), mouse thymocytes (n = 6), and MEFs (n = 1). Different genotypes and/or inhibitors were used.
Project description:During the repair of DNA double-strand breaks (DSBs), de novo synthesized DNA strand can displace the parental strand to generate single-strand DNA (ssDNA) flaps. Many programmed DSBs and thus many ssDNA flaps occur during meiosis. However, how these flaps are removed remains enigmatic. Here, we show that meiosis-specific depletion of Dna2 (dna2-md) in Saccharomyces cerevisiae causes an abundant accumulation of RPA-ssDNA flaps and an expansion of RPA from DSBs to broader regions. As a result, DSB repair is defective and spores are inviable, although the levels of crossovers/non-crossovers seem to be unaffected. Furthermore, inducing Dna2 expression at pachytene is highly effective in removing accumulated RPA and restoring spore viability. Moreover, the depletion of Pif1, an activator of polymerase δ required for meiotic recombination-associated DNA synthesis, and Pif1 inhibitor Mlh2 decreased and increased RPA accumulation in dna2-md, respectively. Together, our findings show that meiotic DSB repair requires Dna2 to remove RPA-ssDNA flaps generated from meiotic recombination-associated DNA synthesis. Additionally, we showed that Dna2 also regulates DSB-independent RPA distribution.
Project description:Eukaryotic cells respond to DNA double-strand breaks (DSBs) by activating a checkpoint that depends on the protein kinases Tel1/ATM and Mec1/ATR. Mec1/ATR is activated by RPA-coated single-stranded DNA (ssDNA), which arises upon nucleolytic degradation (resection) of the DSB. Emerging evidences indicate that RNA processing factors play critical, yet poorly understood, roles in genomic stability. Here, we provide evidence that the Saccharomyces cerevisiae RNA decay factors Xrn1, Rrp6 and Trf4 regulate Mec1/ATR activation by promoting generation of RPA-coated ssDNA. The lack of Xrn1 inhibits ssDNA generation at the DSB by preventing the loading of the MRX complex. By contrast, DSB resection is not affected in the absence of Rrp6 or Trf4, but their lack impairs the recruitment of RPA, and therefore of Mec1, to the DSB. Rrp6 and Trf4 inactivation affects neither Rad51/Rad52 association nor DSB repair by HR, suggesting that full Mec1 activation requires higher amount of RPA-coated ssDNA than HR-mediated repair. Noteworthy, deep transcriptome analyses do not identify common misregulated gene expression that could explain the observed phenotypes. Our results provide a novel link between RNA processing and genome stability. Strand-specific transcriptome analysis of biological replicates of WT cells (JKM139 strain) at T0, or 60 and 240 minutes after HO induction, and of xrn1∆, rrp6∆ and trf4∆ cells at T0.