Chromosomal DNA replication is one of the central biological events occurring inside cells. Due to its large size, the replica-tion of genomic DNA in eukaryotes initiates at hundreds to tens of thousands of sites call...Chromosomal DNA replication is one of the central biological events occurring inside cells. Due to its large size, the replica-tion of genomic DNA in eukaryotes initiates at hundreds to tens of thousands of sites called DNA origins so that the replication could be completed in a limited time. Further, eukaryotic DNA replication is sophisticatedly regulated, and this regulation guarantees that each origin fires once per S phase and each segment of DNA gets duplication also once per cell cycle. The first step of replication initiation is the assembly of pre-replication complex （pre-RC）. Since 1973, four proteins, Cdc6/Cdcl8, MCM, ORC and Cdtl, have been extensively studied and proved to be pre-RC components. Recently, a novel pre-RC compo- nent called Sapl/Girdin was identified. Sapl/Girdin is required for loading Cdcl8/Cdc6 to origins for pre-RC assembly in the fission yeast and human cells, respectively. At the transition of G1 to S phase, pre-RC is activated by the two kinases, cy- clin-dependent kinase （CDK） and Dbf4-dependent kinase （DDK）, and subsequently, RPA, primase-polct, PCNA, topoisomer-ase, Cdc45, polδ and pole are recruited to DNA origins for creating two bi-directional replication forks and initiating DNA replication. As replication forks move along chromatin DNA, they frequently stall due to the presence of a great number of replication barriers on chromatin DNA, such as secondary DNA structures, protein/DNA complexes, DNA lesions, gene tran-scription. Stalled forks must require checkpoint regulation for their stabilization. Otherwise, stalled forks will collapse, which results in incomplete DNA replication and genomic instability. This short review gives a concise introduction regarding the current understanding of replication initiation and replication fork stabilization.展开更多
Homologous recombination （HR） comprises a series of interrelated pathways that function in the repair of DNA double-stranded breaks （DSBs） and interstrand crosslinks （ICLs）. In addition, recombination provides c...Homologous recombination （HR） comprises a series of interrelated pathways that function in the repair of DNA double-stranded breaks （DSBs） and interstrand crosslinks （ICLs）. In addition, recombination provides critical support for DNA replication in the recovery of stalled or broken replication forks, contributing to tolerance of DNA damage. A central core of proteins, most critically the RecA homolog Rad51, catalyzes the key reactions that typify HR： homology search and DNA strand invasion. The diverse functions of recombination are reflected in the need for context-specific factors that perform supplemental functions in conjunction with the core proteins. The inability to properly repair complex DNA damage and resolve DNA replication stress leads to genomic instability and contributes to cancer etiology. Mutations in the BRCA2 recombination gene cause predisposition to breast and ovarian cancer as well as Fanconi anemia, a cancer predisposition syndrome characterized by a defect in the repair of DNA interstrand crosslinks. The cellular functions of recombination are also germane to DNA-based treatment modalities of cancer, which target replicating cells by the direct or indirect induction of DNA lesions that are substrates for recombination pathways. This review focuses on mechanistic aspects of HR relating to DSB and ICL repair as well as replication fork support.展开更多
In archaea, the HEL308 homolog Hel308a（or Hjm） is implicated in stalled replication fork repair. The biochemical properties and structures of Hjm homologs are well documented, but in vivo mechanistic information is ...In archaea, the HEL308 homolog Hel308a（or Hjm） is implicated in stalled replication fork repair. The biochemical properties and structures of Hjm homologs are well documented, but in vivo mechanistic information is limited. Herein, a structure-based functional analysis of Hjm was performed in the genetically tractable hyperthermophilic archaeon, Sulfolobus islandicus. Results showed that domain V and residues within it, which affect Hjm activity and regulation, are essential and that the domain V-truncated mutants and sitedirected mutants within domain V cannot complement hjm chromosomal deletion. Chromosomal hjm deletion can be complemented by ectopic expression of hjm under the control of its native promoter but not an artificial arabinose promoter. Cellular Hjm levels are kept constant under ultraviolet（UV） and methyl methanesulfonate（MMS） treatment conditions in a strain carrying a plasmid to induce Hjm overexpression. These results suggest that Hjm expression and activity are tightly controlled, probably at the translational level.展开更多
Dear Editor,Excessive reactive oxygen species(ROS)cause damage to biomolecules and lead to DNA replication fork slowdown and even stalling(Sies and Jones,2020;Somyajit et al.,2017;Wilhelm et al.,2016);this state is re...Dear Editor,Excessive reactive oxygen species(ROS)cause damage to biomolecules and lead to DNA replication fork slowdown and even stalling(Sies and Jones,2020;Somyajit et al.,2017;Wilhelm et al.,2016);this state is referred to as oxidative stress.Eukaryotic cells employ diverse strategies to maintain redox homeostasis,including the formation of biomolecular condensates through phase separation.展开更多
Deficiencies in DNA damage response and repair not only can result in genome instability and cancer predisposition,but also can render the cancer cells intrinsically more vulnerable to certain types of DNA damage insu...Deficiencies in DNA damage response and repair not only can result in genome instability and cancer predisposition,but also can render the cancer cells intrinsically more vulnerable to certain types of DNA damage insults.Particularly,replication stress is both a hallmark of human cancers and a common instigator for genome instability and cell death.Here,we review our work based on the genetic knockout studies on Blm and Recql5,two members of the mammalian RecQ helicase family.These studies have uncovered a unique partnership between these two helicases in the implementation of proper mitigation strategies under different circum-stances to promote DNA replication and cell survival and suppress genome instability and cancer.In particular,current studies have revealed the presence of a novel Recql5/RECQL5-dependent mechanism for suppressing replication fork collapse in response to global replication fork stalling following exposure to camptothecin(CPT),a topoisomerase I inhibitor,and a potent inhibitor of DNA replication.The unique partnership between Blm and Recql5 in coping with the challenge imposed by replication stress is discussed.In addition,given that irinotecan and topotecan,two CPT derivatives,are currently used in clinic for treating human cancer patients with very promising results,the potential implication of the new findings from these studies in anticancer treatments is also discussed.展开更多
Archaea,the third domain of life,are interesting organisms to study from the aspects of molecular and evolutionary biology.Archaeal cells have a unicellular ultrastructure without a nucleus,resembling bacterial cells,...Archaea,the third domain of life,are interesting organisms to study from the aspects of molecular and evolutionary biology.Archaeal cells have a unicellular ultrastructure without a nucleus,resembling bacterial cells,but the proteins involved in genetic information processing pathways,including DNA replication,transcription,and translation,share strong similarities with those of Eukaryota.Therefore,archaea provide useful model systems to understand the more complex mechanisms of genetic information processing in eukaryotic cells.Moreover,the hyperthermophilic archaea provide very stable proteins,which are especially useful for the isolation of replisomal multicomplexes,to analyze their structures and functions.This review focuses on the history,current status,and future directions of archaeal DNA replication studies.展开更多
文摘Chromosomal DNA replication is one of the central biological events occurring inside cells. Due to its large size, the replica-tion of genomic DNA in eukaryotes initiates at hundreds to tens of thousands of sites called DNA origins so that the replication could be completed in a limited time. Further, eukaryotic DNA replication is sophisticatedly regulated, and this regulation guarantees that each origin fires once per S phase and each segment of DNA gets duplication also once per cell cycle. The first step of replication initiation is the assembly of pre-replication complex （pre-RC）. Since 1973, four proteins, Cdc6/Cdcl8, MCM, ORC and Cdtl, have been extensively studied and proved to be pre-RC components. Recently, a novel pre-RC compo- nent called Sapl/Girdin was identified. Sapl/Girdin is required for loading Cdcl8/Cdc6 to origins for pre-RC assembly in the fission yeast and human cells, respectively. At the transition of G1 to S phase, pre-RC is activated by the two kinases, cy- clin-dependent kinase （CDK） and Dbf4-dependent kinase （DDK）, and subsequently, RPA, primase-polct, PCNA, topoisomer-ase, Cdc45, polδ and pole are recruited to DNA origins for creating two bi-directional replication forks and initiating DNA replication. As replication forks move along chromatin DNA, they frequently stall due to the presence of a great number of replication barriers on chromatin DNA, such as secondary DNA structures, protein/DNA complexes, DNA lesions, gene tran-scription. Stalled forks must require checkpoint regulation for their stabilization. Otherwise, stalled forks will collapse, which results in incomplete DNA replication and genomic instability. This short review gives a concise introduction regarding the current understanding of replication initiation and replication fork stabilization.
文摘Homologous recombination （HR） comprises a series of interrelated pathways that function in the repair of DNA double-stranded breaks （DSBs） and interstrand crosslinks （ICLs）. In addition, recombination provides critical support for DNA replication in the recovery of stalled or broken replication forks, contributing to tolerance of DNA damage. A central core of proteins, most critically the RecA homolog Rad51, catalyzes the key reactions that typify HR： homology search and DNA strand invasion. The diverse functions of recombination are reflected in the need for context-specific factors that perform supplemental functions in conjunction with the core proteins. The inability to properly repair complex DNA damage and resolve DNA replication stress leads to genomic instability and contributes to cancer etiology. Mutations in the BRCA2 recombination gene cause predisposition to breast and ovarian cancer as well as Fanconi anemia, a cancer predisposition syndrome characterized by a defect in the repair of DNA interstrand crosslinks. The cellular functions of recombination are also germane to DNA-based treatment modalities of cancer, which target replicating cells by the direct or indirect induction of DNA lesions that are substrates for recombination pathways. This review focuses on mechanistic aspects of HR relating to DSB and ICL repair as well as replication fork support.
基金supported by the grants from the National Natural Science Foundation of China (Nos. 3093002, 31170072 and 31470184 to Y.S.)
文摘In archaea, the HEL308 homolog Hel308a（or Hjm） is implicated in stalled replication fork repair. The biochemical properties and structures of Hjm homologs are well documented, but in vivo mechanistic information is limited. Herein, a structure-based functional analysis of Hjm was performed in the genetically tractable hyperthermophilic archaeon, Sulfolobus islandicus. Results showed that domain V and residues within it, which affect Hjm activity and regulation, are essential and that the domain V-truncated mutants and sitedirected mutants within domain V cannot complement hjm chromosomal deletion. Chromosomal hjm deletion can be complemented by ectopic expression of hjm under the control of its native promoter but not an artificial arabinose promoter. Cellular Hjm levels are kept constant under ultraviolet（UV） and methyl methanesulfonate（MMS） treatment conditions in a strain carrying a plasmid to induce Hjm overexpression. These results suggest that Hjm expression and activity are tightly controlled, probably at the translational level.
基金funded by grants from the National Natural Science Foundation of China(92254305 and 32130026)。
文摘Dear Editor,Excessive reactive oxygen species(ROS)cause damage to biomolecules and lead to DNA replication fork slowdown and even stalling(Sies and Jones,2020;Somyajit et al.,2017;Wilhelm et al.,2016);this state is referred to as oxidative stress.Eukaryotic cells employ diverse strategies to maintain redox homeostasis,including the formation of biomolecular condensates through phase separation.
文摘Deficiencies in DNA damage response and repair not only can result in genome instability and cancer predisposition,but also can render the cancer cells intrinsically more vulnerable to certain types of DNA damage insults.Particularly,replication stress is both a hallmark of human cancers and a common instigator for genome instability and cell death.Here,we review our work based on the genetic knockout studies on Blm and Recql5,two members of the mammalian RecQ helicase family.These studies have uncovered a unique partnership between these two helicases in the implementation of proper mitigation strategies under different circum-stances to promote DNA replication and cell survival and suppress genome instability and cancer.In particular,current studies have revealed the presence of a novel Recql5/RECQL5-dependent mechanism for suppressing replication fork collapse in response to global replication fork stalling following exposure to camptothecin(CPT),a topoisomerase I inhibitor,and a potent inhibitor of DNA replication.The unique partnership between Blm and Recql5 in coping with the challenge imposed by replication stress is discussed.In addition,given that irinotecan and topotecan,two CPT derivatives,are currently used in clinic for treating human cancer patients with very promising results,the potential implication of the new findings from these studies in anticancer treatments is also discussed.
基金supported in part by the Human Frontier Science Programseveral research grants from Ministry of Education,Culture, Sports, Science, and Technology of Japan+1 种基金the Japan New Energy and Industrial Technology Development Organizationthe Japan Science and Technology Agency
文摘Archaea,the third domain of life,are interesting organisms to study from the aspects of molecular and evolutionary biology.Archaeal cells have a unicellular ultrastructure without a nucleus,resembling bacterial cells,but the proteins involved in genetic information processing pathways,including DNA replication,transcription,and translation,share strong similarities with those of Eukaryota.Therefore,archaea provide useful model systems to understand the more complex mechanisms of genetic information processing in eukaryotic cells.Moreover,the hyperthermophilic archaea provide very stable proteins,which are especially useful for the isolation of replisomal multicomplexes,to analyze their structures and functions.This review focuses on the history,current status,and future directions of archaeal DNA replication studies.
