Checkpoint adaptor protein. Probable component of replication forks.




Claspin (Xl, Hs)


Molecular weight

124 kDa (Sc)


Biochemical properties

•DNA binding of oligos (1) and branched structures (2)



• phosphopeptide motifs (chk1 site) (3)

Protein interactions


•Cdc45 (4) (5) tethers to stalled forks?

•Mcm2/3 (6) (7)

•Synthetic lethality pola (7)

• in GINS complex (8)

• Synthetic lethality rrm1

• pol2 separate sites at n and c termini modulated by Dpb2{Lou et al., 2008, Mol Cell, 32, 106-17}



•Cds1 – needed to recruit cds1 to stalled forks

(9) (10)



• Chk1 (Binds and activates) in xenopus extracts (11) binding region (12) the interaction needs topbp1 (13)

• plx (14) in aphididcolin or uv conditions. (modified by kinase)

•BRCA1 complex (15)



• PCNA (16)

•human homologues of c elegans clk2 (17)

•Rad17 (phosphorylated) (18)

• cdc7 in chk1 activation{Kim et al., 2008, Oncogene, 27, 3475-82}



• Phosphorylation via mec1 (6) (19) . Tel2 needed for its phosp (20) horylation



•phosphorylated if add synthetic oligos or aphidicolin/uv  into extracts (11) or hu (h) (21) site in chk1 interaction domain (22)

•ub for degradation via proteosome. (22)



• phosphorylated chk1  mediates function (3) , and is needed for clasp in stability (23)

• phosphorylated by cdc7 (24)


• Ring structure



Cellular location and expression


•Binds to origins the moves away with sites BrdU incorporation (4) (19) (5) loads independently of tof



•Expression up in g1/s peaks g2/m (21) rapid drop off in M (22) levels up on hu, v or aphidicolin in ATR dependent way

• proteolysis by SCFbetaTrCP in recovery from damage (25) (26) . Some role for plk1 in this process (27) . controlled by de ub enzyme USP7 {Faustrup et al., 2009, J Cell Biol, 184, 13-9}

• apc substrate in g1 degradation prevented by de ubitylation by usp28 {Bassermann et al., 2008, Cell, 134, 256-67}

Other comments


• transduces replication stress through rad53 (28)

•Present at rfbs (29) although not needed at all rfbs

•mutants give defective fork movement in normal cell cycle (6) (30) (31) and faulty pausing in tRNA genes tof doesn’t do this)

•mutants don’t activate the checkpoint for genotoxic drugs (30)

• needed for telomere end protection after loss of capping (32) (33)

• regulates crossing over (34)

•Important for triplet repeat stability {Razidlo and Lahue, 2008, DNA Repair (Amst), 7, 633-40}



• transduces replication stress through cds1

(28) •Not needed for replication fork pausing here

• regulates replication machinery (35)



•Needs cdc45 to load on chromatin


•slight negative effect of rad17/atr on binding in the presence aphidicolin.



•Overexpression (h) gives increased cell proliferation (15)

• regulates ddb2 (36)

•Needed for ATR activation of chk1 acts through claspin {Bennett et al., 2008, Biochem Biophys Res Commun, 369, 973-6}

• slowing of fork progression in claspin depleted cells {Petermann et al., 2008, Mol Biol Cell, 19, 2373-8}

• needed for ub PCNA after DNA damage {Yang et al., 2008, Genes Dev, 22, 1147-52}


Revised by


Last edited

14 July 09



1.    Yoo,H.Y., Jeong,S.Y. and Dunphy,W.G. (2006) Site-specific phosphorylation of a checkpoint mediator protein controls its responses to different DNA structures. Genes Dev 20, 772-783.

2.    Sar,F., Lindsey-Boltz,L.A., Subramanian,D., Croteau,D.L., Hutsell,S.Q., Griffith,J.D. and Sancar,A. (2004) Human claspin is a ring-shaped DNA-binding protein with high affinity to branched DNA structures. J Biol Chem279, 39289-39295.

3.    Chini,C.C. and Chen,J. (2006) Repeated phosphopeptide motifs in human Claspin are phosphorylated by Chk1 and mediate Claspin function. J Biol Chem 281, 33276-33282.

4.    Katou,Y., Kanoh,Y., Bando,M., Noguchi,H., Tanaka,H., Ashikari,T., Sugimoto,K. and Shirahige,K. (2003) S-phase checkpoint proteins Tof1 and Mrc1 form a stable replication-pausing complex. Nature 424, 1078-1083.

5.    Zegerman,P. and Diffley,J.F. (2003) Lessons in how to hold a fork. Nat Struct Biol 10, 778-779.

6.    Szyjka,S.J., Viggiani,C.J. and Aparicio,O.M. (2005) Mrc1 is required for normal progression of replication forks throughout chromatin in S. cerevisiae. Mol Cell 19, 691-697.

7.    Nedelcheva,M.N., Roguev,A., Dolapchiev,L.B., Shevchenko,A., Taskov,H.B., Shevchenko,A., Stewart,A.F. and Stoynov,S.S. (2005) Uncoupling of unwinding from DNA synthesis implies regulation of MCM helicase by Tof1/Mrc1/Csm3 checkpoint complex. J Mol Biol 347, 509-521.

8.    Gambus,A., Jones,R.C., Sanchez-Diaz,A., Kanemaki,M., van Deursen,F., Edmondson,R.D. and Labib,K. (2006) GINS maintains association of Cdc45 with MCM in replisome progression complexes at eukaryotic DNA replication forks. Nat Cell Biol 8, 358-366.

9.    Xu,Y.J., Davenport,M. and Kelly,T.J. (2006) Two-stage mechanism for activation of the DNA replication checkpoint kinase Cds1 in fission yeast. Genes Dev 20, 990-1003.

10.  Tanaka,K. and Russell,P. (2004) Cds1 phosphorylation by Rad3-Rad26 kinase is mediated by forkhead-associated domain interaction with Mrc1. J Biol Chem 279, 32079-32086.

11.  Lee,J., Kumagai,A. and Dunphy,W.G. (2003) Claspin, a Chk1-regulatory protein, monitors DNA replication on chromatin independently of RPA, ATR, and Rad17. Mol Cell 11, 329-340.

12.  Kumagai,A. and Dunphy,W.G. (2003) Repeated phosphopeptide motifs in Claspin mediate the regulated binding of Chk1. Nat Cell Biol 5, 161-165.

13.  Liu,S., Bekker-Jensen,S., Mailand,N., Lukas,C., Bartek,J. and Lukas,J. (2006) Claspin operates downstream of TopBP1 to direct ATR signaling towards Chk1 activation. Mol Cell Biol 26, 6056-6064.

14.  Yoo,H.Y., Kumagai,A., Shevchenko,A., Shevchenko,A. and Dunphy,W.G. (2004) Adaptation of a DNA replication checkpoint response depends upon inactivation of Claspin by the Polo-like kinase. Cell 117, 575-588.

15.  Lin,S.Y., Li,K., Stewart,G.S. and Elledge,S.J. (2004) Human Claspin works with BRCA1 to both positively and negatively regulate cell proliferation. Proc Natl Acad Sci U S A 101, 6484-6489.

16.  Brondello,J.M., Ducommun,B., Fernandez,A. and Lamb,N.J. (2007) Linking PCNA-dependent replication and ATR by human Claspin. Biochem Biophys Res Commun 354, 1028-1033.

17.  Collis,S.J., Barber,L.J., Clark,A.J., Martin,J.S., Ward,J.D. and Boulton,S.J. (2007) HCLK2 is essential for the mammalian S-phase checkpoint and impacts on Chk1 stability. Nat Cell Biol 9, 391-401.

18.  Wang,X., Zou,L., Lu,T., Bao,S., Hurov,K.E., Hittelman,W.N., Elledge,S.J. and Li,L. (2006) Rad17 phosphorylation is required for claspin recruitment and Chk1 activation in response to replication stress. Mol Cell 23, 331-341.

19.  Osborn,A.J. and Elledge,S.J. (2003) Mrc1 is a replication fork component whose phosphorylation in response to DNA replication stress activates Rad53. Genes Dev 17, 1755-1767.

20.  Shikata,M., Ishikawa,F. and Kanoh,J. (2007) Tel2 is required for activation of the Mrc1-mediated replication checkpoint. J Biol Chem 282, 5346-5355.

21.  Chini,C.C. and Chen,J. (2003) Human claspin is required for replication checkpoint control. J Biol Chem 278, 30057-30062.

22.  Bennett,L.N. and Clarke,P.R. (2006) Regulation of Claspin degradation by the ubiquitin-proteosome pathway during the cell cycle and in response to ATR-dependent checkpoint activation. FEBS Lett 580, 4176-4181.

23.  Chini,C.C., Wood,J. and Chen,J. (2006) Chk1 is required to maintain claspin stability. Oncogene 25, 4165-4171.

24.  Kim,J.M., Kakusho,N., Yamada,M., Kanoh,Y., Takemoto,N. and Masai,H. (2007) Cdc7 kinase mediates Claspin phosphorylation in DNA replication checkpoint. Oncogene

25.  Mailand,N., Bekker-Jensen,S., Bartek,J. and Lukas,J. (2006) Destruction of Claspin by SCFbetaTrCP restrains Chk1 activation and facilitates recovery from genotoxic stress. Mol Cell 23, 307-318.

26.  Peschiaroli,A., Dorrello,N.V., Guardavaccaro,D., Venere,M., Halazonetis,T., Sherman,N.E. and Pagano,M. (2006) SCFbetaTrCP-mediated degradation of Claspin regulates recovery from the DNA replication checkpoint response. Mol Cell 23, 319-329.

27.  Mamely,I., van Vugt,M.A., Smits,V.A., Semple,J.I., Lemmens,B., Perrakis,A., Medema,R.H. and Freire,R. (2006) Polo-like kinase-1 controls proteasome-dependent degradation of Claspin during checkpoint recovery. Curr Biol 16, 1950-1955.

28.  Alcasabas,A.A., Osborn,A.J., Bachant,J., Hu,F., Werler,P.J., Bousset,K., Furuya,K., Diffley,J.F., Carr,A.M. and Elledge,S.J. (2001) Mrc1 transduces signals of DNA replication stress to activate Rad53. Nat Cell Biol 3, 958-965.

29.  Calzada,A., Hodgson,B., Kanemaki,M., Bueno,A. and Labib,K. (2005) Molecular anatomy and regulation of a stable replisome at a paused eukaryotic DNA replication fork. Genes Dev 19, 1905-1919.

30.  Tourriere,H., Versini,G., Cordon-Preciado,V., Alabert,C. and Pasero,P. (2005) Mrc1 and Tof1 promote replication fork progression and recovery independently of Rad53. Mol Cell 19, 699-706.

31.  Hodgson,B., Calzada,A. and Labib,K. (2007) Mrc1 and Tof1 regulate DNA replication forks in different ways during normal S phase. Mol Biol Cell 18, 3894-3902.

32.  Grandin,N. and Charbonneau,M. (2007) Mrc1, a non-essential DNA replication protein, is required for telomere end protection following loss of capping by Cdc13, Yku or telomerase. Mol Genet Genomics 277, 685-699.

33.  Tsolou,A. and Lydall,D. (2007) Mrc1 protects uncapped budding yeast telomeres from exonuclease EXO1. DNA Repair (Amst) 6, 1607-1617.

34.  Robert,T., Dervins,D., Fabre,F. and Gangloff,S. (2006) Mrc1 and Srs2 are major actors in the regulation of spontaneous crossover. EMBO J 25, 2837-2846.

35.  Nitani,N., Nakamura,K., Nakagawa,C., Masukata,H. and Nakagawa,T. (2006) Regulation of DNA replication machinery by Mrc1 in fission yeast. Genetics 174, 155-165.

36.  Praetorius-Ibba,M., Wang,Q.E., Wani,G., El-Mahdy,M.A., Zhu,Q., Qin,S. and Wani,A.A. (2007) Role of Claspin in regulation of nucleotide excision repair factor DDB2. DNA Repair (Amst) 6, 578-587.