DNA Damage-dependent and -independent Phosphorylation of the hRad9 Checkpoint Protein

Cell cycle checkpoints are regulatory mechanisms that maintain genomic integrity by preventing cell cycle progression when genetic anomalies are present. The hRad9 protein is the human homologue of Schizosaccharomyces pombe Rad9, a checkpoint protein required for preventing the onset of mitosis if DNA damage is present or if DNA replication is incomplete. Genetic and biochemical analyses indicate that hRad9 is a component of the checkpoint response in humans and has possible roles in regulating the cell cycle, apoptosis, and DNA repair. Previous studies indicate that hRad9 is modified by phosphorylation, both in the absence of exogenous stress and in response to various genotoxins. In this study, we report the mapping of several sites of constitutive phosphorylation of hRad9 to (S/T)P X(R/P) sequences near the C terminus of the protein. We also demonstrate that a serine to alanine mutation at residue 272 abrogates an ionizing radiation (IR)-induced phosphorylation of hRad9 and further show that phosphorylation at (S/T)P sites is not a prerequisite for IR-induced phosphorylation of serine 272. Finally, we report that hRad9 undergoes cell cycle-regulated hyper-phosphorylation in G2/M that is enhanced by IR but distinct from that on serine 272. Unlike the IR-induced phosphorylation at serine 272, this event is dependent on serine 277 and threonine 292, two C-terminal (S/T)P sites in hRad9. Cell cycle checkpoints are regulatory mechanisms that maintain genomic integrity by preventing cell cycle progression when genetic anomalies are present. The hRad9 protein is the human homologue of Schizosaccharomyces pombe Rad9, a checkpoint protein required for preventing the onset of mitosis if DNA damage is present or if DNA replication is incomplete. Genetic and biochemical analyses indicate that hRad9 is a component of the checkpoint response in humans and has possible roles in regulating the cell cycle, apoptosis, and DNA repair. Previous studies indicate that hRad9 is modified by phosphorylation, both in the absence of exogenous stress and in response to various genotoxins. In this study, we report the mapping of several sites of constitutive phosphorylation of hRad9 to (S/T)P X(R/P) sequences near the C terminus of the protein. We also demonstrate that a serine to alanine mutation at residue 272 abrogates an ionizing radiation (IR)-induced phosphorylation of hRad9 and further show that phosphorylation at (S/T)P sites is not a prerequisite for IR-induced phosphorylation of serine 272. Finally, we report that hRad9 undergoes cell cycle-regulated hyper-phosphorylation in G2/M that is enhanced by IR but distinct from that on serine 272. Unlike the IR-induced phosphorylation at serine 272, this event is dependent on serine 277 and threonine 292, two C-terminal (S/T)P sites in hRad9. proliferating cell nuclear antigen Dulbecco's modified Eagle's medium retinal pigment epithelial human telomerase reverse transcriptase subunit fetal bovine serum phosphate-buffered saline calf intestinal phosphatase polyacrylamide gel electrophoresis ionizing radiation An organism's genome is under constant stress from a variety of endogenous and exogenous sources. Although low frequencies of genetic mutation are tolerated, contributing to genetic diversity, high frequencies are harmful and can lead to cancer (1Loeb L.A. Cancer Res. 1991; 51: 3075-3079PubMed Google Scholar). At the cellular level, eukaryotes have evolved signal transduction pathways called checkpoints to cope with genetic insults (2Hartwell L.H. Weinert T.A. Science. 1989; 246: 629-634Crossref PubMed Scopus (2413) Google Scholar, 3Weinert T.A. Hartwell L.H. Science. 1988; 241: 317-322Crossref PubMed Scopus (947) Google Scholar, 4Hartwell L. Cell. 1992; 71: 543-546Abstract Full Text PDF PubMed Scopus (737) Google Scholar). Checkpoints stall progression through the cell cycle, providing time for cellular responses such as activation and re-localization of DNA repair enzymes to sites of DNA damage or transcriptional activation of specific genes. Checkpoint arrest can also lead to activation of apoptotic pathways perhaps under conditions when cell death is more beneficial to the organism as a whole than repair (reviewed in Refs. 5Elledge S.J. Science. 1996; 274: 1664-1672Crossref PubMed Scopus (1760) Google Scholar, 6Weinert T. Curr. Opin. Genet. Dev. 1998; 8: 185-193Crossref PubMed Scopus (174) Google Scholar, 7Zhou B.B. Elledge S.J. Nature. 2000; 408: 433-439Crossref PubMed Scopus (2625) Google Scholar). The hRad9 gene was first identified based on sequence homology to the rad9+ gene of the fission yeast Schizosaccharomyces pombe (8Lieberman H.B. Hopkins K.M. Nass M. Demetrick D. Davey S. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 13890-13895Crossref PubMed Scopus (107) Google Scholar). In S. pombe,rad9+ is required for the S-phase and G2 checkpoints, which delay the onset of mitosis if DNA replication is incomplete or if DNA damage is present, respectively (3Weinert T.A. Hartwell L.H. Science. 1988; 241: 317-322Crossref PubMed Scopus (947) Google Scholar,9Enoch T. Nurse P. Cell. 1990; 60: 665-673Abstract Full Text PDF PubMed Scopus (343) Google Scholar, 10Enoch T. Carr A.M. Nurse P. Genes Dev. 1992; 6: 2035-2046Crossref PubMed Scopus (307) Google Scholar, 11al-Khodairy F. Carr A.M. EMBO J. 1992; 11: 1343-1350Crossref PubMed Scopus (367) Google Scholar, 12al-Khodairy F. Fotou E. Sheldrick K.S. Griffiths D.J. Lehmann A.R. Carr A.M. Mol. Biol. Cell. 1994; 5: 147-160Crossref PubMed Scopus (317) Google Scholar, 13Rowley R. Subramani S. Young P.G. EMBO J. 1992; 11: 1335-1342Crossref PubMed Scopus (187) Google Scholar). Five other S. pombe genes,hus1+, rad1+,rad3+, rad17+, and rad26+ are also required for this response (10Enoch T. Carr A.M. Nurse P. Genes Dev. 1992; 6: 2035-2046Crossref PubMed Scopus (307) Google Scholar, 11al-Khodairy F. Carr A.M. EMBO J. 1992; 11: 1343-1350Crossref PubMed Scopus (367) Google Scholar, 12al-Khodairy F. Fotou E. Sheldrick K.S. Griffiths D.J. Lehmann A.R. Carr A.M. Mol. Biol. Cell. 1994; 5: 147-160Crossref PubMed Scopus (317) Google Scholar, 13Rowley R. Subramani S. Young P.G. EMBO J. 1992; 11: 1335-1342Crossref PubMed Scopus (187) Google Scholar) and are also, with the exception of rad26+, conserved in humans (14Cimprich K.A. Shin R.B. Keith C.T. Schreiber S.L. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 2850-2855Crossref PubMed Scopus (225) Google Scholar, 15Kostrub C.F. Knudsen K. Subramani S. Enoch T. Kostrub C.F. Knudsen K. Subramani S. Enoch T. EMBO J. 1998; 17: 2055-2066Crossref PubMed Scopus (100) Google Scholar, 16Parker A.E. Van de Weyer I. Laus M.C. Verhasselt P. Luyten W.H. J. Biol. Chem. 1998; 273: 18340-18346Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar, 17Udell C.M. Lee S.K. Davey S. Nucleic Acids Res. 1998; 26: 3971-3978Crossref PubMed Scopus (35) Google Scholar). Like their S. pombe orthologues, hRad9, hRad1, and hHus1, interact with each other in a stable complex (15Kostrub C.F. Knudsen K. Subramani S. Enoch T. Kostrub C.F. Knudsen K. Subramani S. Enoch T. EMBO J. 1998; 17: 2055-2066Crossref PubMed Scopus (100) Google Scholar, 18Volkmer E. Karnitz L.M. J. Biol. Chem. 1999; 274: 567-570Abstract Full Text Full Text PDF PubMed Scopus (176) Google Scholar, 19St. Onge R.P. Udell C.M. Casselman R. Davey S. Mol. Biol. Cell. 1999; 10: 1985-1995Crossref PubMed Scopus (129) Google Scholar, 20Hang H. Lieberman H.B. Genomics. 2000; 65: 24-33Crossref PubMed Scopus (56) Google Scholar) that has recently been dubbed the 9-1-1 complex (21Burtelow M.A. Roos-Mattjus P.M. Rauen M. Babendure J.R. Karnitz L.M. J. Biol. Chem. 2001; 276: 25903-25909Abstract Full Text Full Text PDF PubMed Scopus (116) Google Scholar). Structural homology between each member of the 9-1-1 complex and PCNA has led to the hypothesis that the 9-1-1 complex replaces replication-associated PCNA-dependent functions during DNA repair (22Caspari T. Dahlen M. Kanter-Smoler G. Lindsay H.D. Hofmann K. Papadimitriou K. Sunnerhagen P. Carr A.M. Mol. Cell. Biol. 2000; 20: 1254-1262Crossref PubMed Scopus (207) Google Scholar, 23Thelen M.P. Venclovas C. Fidelis K. Cell. 1999; 96: 769-770Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar, 24Venclovas C. Thelen M.P. Nucleic Acids Res. 2000; 28: 2481-2493Crossref PubMed Scopus (230) Google Scholar). During DNA replication, the PCNA homotrimer forms a ring-like sliding clamp over DNA and acts to increase the processivity of DNA polymerase δ (25Bravo R. Frank R. Blundell P.A. Macdonald-Bravo H. Nature. 1987; 326: 515-517Crossref PubMed Scopus (1637) Google Scholar, 26Krishna T.S. Kong X.P. Gary S. Burgers P.M. Kuriyan J. Cell. 1994; 79: 1233-1243Abstract Full Text PDF PubMed Scopus (750) Google Scholar). The 9-1-1/PCNA model is supported by the observation that hRad9, hRad1, and hHus1 each interact with hRad17 (27Rauen M. Burtelow M.A. Dufault V.M. Karnitz L.M. J. Biol. Chem. 2000; 275: 29767-29771Abstract Full Text Full Text PDF PubMed Scopus Google which homology to of replication a protein required for DNA (reviewed in R. U. 1998; Google Scholar). DNA damage not the phosphorylation of hRad9 and but also the of 9-1-1 with M.A. Karnitz L.M. J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Scopus Google Scholar). this an model has in which of 9-1-1 DNA at sites of damage the checkpoint Although that hRad17 and 9-1-1 are of the are for the of DNA damage In S. the a in response to DNA damage of the other checkpoint Carr A.M. Cell Biol. 1999; PubMed Scopus Google that is the of the checkpoint human of and a variety of cellular on sequences in response to DNA damage S. G. A. K. Elledge S.J. Proc. Natl. Acad. Sci. U. S. A. 2000; PubMed Scopus Google Scholar, D. J. Elledge S.J. Science. 1999; PubMed Scopus Google Scholar, J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus Google Scholar, S. L. S. L. C. Science. 1998; PubMed Scopus Google Scholar, K.A. K. K. E. Science. 1998; PubMed Scopus Google Scholar, D. K.M. R. D. Elledge S.J. Genes Dev. 2000; PubMed Scopus Google Scholar, J. Cancer Res. 2000; 60: Google Scholar, K.M. C. Genes Dev. 1999; PubMed Scopus Google Scholar). in in the cancer K. A. S. G. L. S. T. S. M. I. M. R. A. A. L. C.F. T. M. Science. PubMed Scopus Google Scholar). hRad9 has been as an Lieberman H.B. G. Lee J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). Although the from fission yeast indicate that hRad9 is a in the G2/M F. Carr A.M. EMBO J. 1992; 11: 1343-1350Crossref PubMed Scopus (367) Google phosphorylation of hRad9 of cell cycle and to for the damage checkpoint Lieberman H.B. G. Lee J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). hRad9, through with the and can also to have a in to K. T. H. Hopkins K.M. S. M. Lieberman H.B. Cell Biol. 2000; PubMed Scopus Google Scholar). Previous studies indicate that the hRad9 protein is modified by phosphorylation under cellular conditions Onge R.P. Udell C.M. Casselman R. Davey S. Mol. Biol. Cell. 1999; 10: 1985-1995Crossref PubMed Scopus (129) Google Scholar) and in response to DNA damage at serine 272 E. Karnitz L.M. J. Biol. Chem. 1999; 274: 567-570Abstract Full Text Full Text PDF PubMed Scopus (176) Google Scholar, Lieberman H.B. G. Lee J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). we further the of hRad9 phosphorylation by mapping sites required for constitutive phosphorylation and by of a cell ionizing phosphorylation The hRad9 was and sites of the from is by the constitutive of the and a of the of human M. J. P. K. K. M. Mol. Cell. Biol. 1988; 8: PubMed Google Scholar). hRad9 in the to the to and sites in The sequence of and the hRad9 are in with by or by in the The of the by DNA an DNA and of for hRad9 to in a in modified medium with fetal bovine serum at in The cell a human retinal pigment cell that the human telomerase reverse transcriptase subunit was as in in or or of a of and The was with of DNA in of or in of and to for at The was with and for an as in S-phase by as H. Mol. Cell. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). to a of and with for from for for an and for of in S-phase a of by with cell by in of and by the of of and at for at in in of and and for at by and in and and a in of with and on for and at by the of of for at The was with of 19St. Onge R.P. Udell C.M. Casselman R. Davey S. Mol. Biol. Cell. 1999; 10: 1985-1995Crossref PubMed Scopus (129) Google and of for at with of and in of and for and at for of was in the of of calf intestinal phosphatase in in a of for at The was by the of of in a as the with for in and saline to with of and of further at in for with and with and with a cell by at for The was and the in of and on for at for at cell with hRad9 as was with in of electrophoresis and for The gel was to and with hRad9 or a gel of the was and a was and a for electrophoresis through or as to a cell or a for in in and in at in for at in in at a of in for at and in to The hRad9 protein is in the absence of DNA damage Onge R.P. Udell C.M. Casselman R. Davey S. Mol. Biol. Cell. 1999; 10: 1985-1995Crossref PubMed Scopus (129) Google Scholar) and when DNA damage is present E. Karnitz L.M. J. Biol. Chem. 1999; 274: 567-570Abstract Full Text Full Text PDF PubMed Scopus (176) Google Scholar). We have that under cellular conditions are not to exogenous hRad9 of that in on as by The of which we have with the of endogenous hRad9 at an of In of exogenous hRad9 each of forms to a at which we have called that to endogenous hRad9, a of the protein is has various We have of forms Previous in has that the C terminus of exogenous hRad9 can the of from to P. and S. that the C terminus of hRad9 is required for constitutive phosphorylation of the protein. this in we to required for the constitutive phosphorylation of hRad9. near the C terminus of the protein to in and for as by The of protein by the to hRad9 protein from the endogenous protein by the time to between with as each of serine or threonine by a in The (S/T)P is the sequence for the of Curr. Opin. Biol. 1999; PubMed Scopus Google Scholar). We (S/T)P sequences in hRad9, from and their to the protein the (S/T)P in hRad9 on that are sites of The and of two The mutation an increase in of of the the mutation a in of the and forms by with calf intestinal each protein at that the in the are the of phosphorylation in to a in the of forms and a increase in the of hRad9 Although the protein as a as a with than from the mutation is with that in C as as and with an of which is than the of for of hRad9 phosphorylation in the residue of in from phosphorylation at the residue of the residue of in from phosphorylation at the residue of in a The a when with phosphatase the of sites of constitutive phosphorylation in hRad9. sites (S/T)P sites phosphorylation or on a we (S/T)P sites in hRad9 in The of the and and was not from that of the and was to phosphatase on at (S/T)P hRad9 is also on sites other than We have called the of hRad9, which phosphorylation at (S/T)P sites but further the constitutive phosphorylation of hRad9, with a of hRad9 or and with The hRad9 and in the and the hRad9 protein was from protein was by to and with hRad9 The of hRad9 protein from each was by of the a and was for as gel was also to a and a In with each hRad9 was that the hRad9 protein is at sites other than (S/T)P We on to the signal in the to in each and to protein by of the hRad9 the was at threonine a we to we that have a signal than each of the other and The in which a of to the such as protein than in and two DNA that in the biochemical as hRad9, have been to at sequences J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus Google Scholar). serine 272 of hRad9 is by a we that this was the of the ionizing radiation (IR)-induced phosphorylation of hRad9 E. Karnitz L.M. J. Biol. Chem. 1999; 274: 567-570Abstract Full Text Full Text PDF PubMed Scopus (176) Google Scholar). In this we that a serine to alanine mutation at serine 272 on constitutive phosphorylation but the of hRad9 to in response to ionizing radiation Although of both the and forms of hRad9 a when with and of IR to and to the in or was to the of phosphorylation, of Although the of the with the complex of hRad9 has this to by we have this to and further in of in and C. observation also a report that that ionizing radiation phosphorylation at this residue and that this phosphorylation was Lieberman H.B. G. Lee J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). studies IR-induced phosphorylation of hRad9, a protein Although the of this constitutive phosphorylation of hRad9 cellular The observation in that the forms of hRad9, the in response to to indicate that (S/T)P phosphorylation of hRad9 is not required for IR-induced phosphorylation at serine 272. this we the response to IR of hRad9 which (S/T)P The hRad9 was in that or was from with phosphatase as by and with hRad9 In response to a of and in and when with that was in a of that the IR-induced phosphorylation of was at serine 272, the mutation was the and for to low and high of IR with the as a at time of the was at The of this was not when the mutation was the At the of this was and not as a response of checkpoint indicate that constitutive phosphorylation at (S/T)P sites is not for the IR-induced phosphorylation of hRad9 at serine 272. that hRad9 is on we that the of constitutive in a cell a was to cell which for in endogenous hRad9 phosphorylation by Cell cycle was by of with a report Lieberman H.B. G. Lee J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google which we have to at C-terminal (S/T)P was in of the cell cycle forms of hRad9, at an of in during G2/M and We on to demonstrate that this was the of a cell phosphorylation event the and in G2/M a at this phosphorylation was in or S-phase with of IR to delay in with the to arrest in or and to cycle with in the the was present in G2 and but not when first with a low of IR or not and time indicate that in endogenous hRad9 is in G2 and mitosis on an distinct from the constitutive phosphorylation sites we have that the cell cycle-regulated hyper-phosphorylation of hRad9 was distinct from that by high of ionizing radiation at serine 272, with of IR at various of the cell cycle their with and the of Lieberman H.B. G. Lee J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google in was that endogenous hRad9 was in a in response to ionizing radiation of cell cycle The of and was distinct from in G2/M and time the of was if with ionizing radiation at time and to a when in the cell cycle-regulated phosphorylation of hRad9 was cell in we this in have an to stable of the human telomerase reverse transcriptase subunit but maintain the of epithelial in hRad9 in the a in response to IR at of the cell cycle in G2/M was in the absence of IR with that for the cell the of and that hRad9 undergoes cell IR-induced phosphorylation in both and the cell cycle-regulated hyper-phosphorylation of hRad9 was dependent on phosphorylation at (S/T)P we each of the (S/T)P in and for the cell we in the endogenous protein and The was also in this in mitosis by with and with hRad9 The absence of signal in the that from the protein and not endogenous hRad9. was to the of the In each of the cell in an increase in the of in G2/M from in the to in the in a in the of the the of the protein as two that through than the from are to the forms in the G2/M of A. The cell hyper-phosphorylation of hRad9 was also in the protein as as each of the (S/T)P with two the serine 277 is to the of this hyper-phosphorylation is of the protein with the in the of threonine in the of the and the of the hRad9 at (S/T)P sites (S/T)P sites but serine 277 was and the protein was when of the mutation in and the of this hyper-phosphorylation was as was for the the mutation was the and and the hyper-phosphorylation was the was for the which hRad9 (S/T)P We have that are in the hRad9 checkpoint protein. serine serine and threonine when to the of hRad9 in in a that is with phosphorylation of the we have identified is by in the sequence of hRad9. on this the sites in hRad9 to the of the (S/T)P as a in The of is at serine 277 of hRad9 at which by J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google is in each of the constitutive hRad9 sites we have identified and 292, which we to required for the cell phosphorylation of hRad9 the other hRad9 (S/T)P with a at The (S/T)P sequences in the protein serine serine and serine at in to that not the of hRad9 through and or in that sites are not Although we have the (S/T)P phosphorylation sites we the that phosphorylation at sites is in a complex cell and have as we have that endogenous hRad9 as a at on a we have in the when endogenous hRad9 that with the of the protein we are to the of by the of phosphatase in or by in we the that hRad9 are in the at of the cell cycle and and that phosphorylation at serine serine serine and threonine constant the cell a the serine 272 of hRad9 was to demonstrate that IR-induced phosphorylation of hRad9 at this in Lieberman H.B. G. Lee J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). We have an by that a serine to alanine mutation at residue 272 abrogates hRad9 phosphorylation when are a high of IR The observation by Lieberman H.B. G. Lee J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar) that phosphorylation at this residue is dependent on the of IR-induced DNA damage and the of the checkpoint response in In further with the of Lieberman H.B. G. Lee J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar) is observation that phosphorylation at serine 272 of cell cycle and and of indicate that this of (S/T)P phosphorylation as when are with high of in both the and forms of hRad9 are that are not in a of the (S/T)P phosphorylation sites a protein that is of serine 272 phosphorylation in response to IR and We also report the a hyper-phosphorylation event for hRad9 that is cell We first identified in that been in G2 or mitosis and that we increase their by with ionizing In we that a human epithelial cell in G2 and at this cell cycle The for this is that in the absence of the endogenous DNA damage to the checkpoint in the absence of IR this cell cycle-regulated and DNA phosphorylation event is in on we can that the cell cycle-regulated phosphorylation of hRad9 at a other than we have identified as constitutive phosphorylation sites serine serine or threonine and not on the IR-induced phosphorylation at serine 272. Although phosphorylation at serine 272 is of cell cycle and (S/T)P phosphorylation, the cell cycle-regulated phosphorylation of hRad9 is dependent on both cell cycle and constitutive (S/T)P a mutation not the constitutive phosphorylation of hRad9 but also to cell cycle-regulated hyper-phosphorylation when are in mitosis of the other constitutive sites we have identified not this of serine serine and threonine or in a protein of cell cycle-regulated hyper-phosphorylation threonine with abrogates of the G2/M of hRad9 and the of the other threonine is the (S/T)P that is conserved between hRad9 and S. pombe Carr A.M. Lehmann A.R. Nucleic Acids Res. 1991; PubMed Scopus Google Scholar). The of of the forms in a indicate that threonine is in An is that threonine is serine is a prerequisite for hyper-phosphorylation of hRad9. Although the mutation under conditions and a in was in with and the cell cycle-regulated hyper-phosphorylation is dependent on threonine 292, further required to the of this of further is the observation that the that of the when the protein is are but during a arrest the of or further phosphorylation of at the G2/M this has to the endogenous which in the to has been recently that the of hRad9 with and hHus1 in the of a ring-like that the DNA Although the of this complex has to the sequence of indicate to the PCNA a ring-like complex that acts as a sliding clamp over In the of and hHus1 are but the first of hRad9 the model C. Thelen M.P. Nucleic Acids Res. 2000; 28: 2481-2493Crossref PubMed Scopus (230) Google Scholar). The and (S/T)P sites for hRad9 phosphorylation sites we have are at the of this 272 and serine or C-terminal to 292, serine serine and threonine that phosphorylation at for 9-1-1 E. Karnitz L.M. J. Biol. Chem. 1999; 274: 567-570Abstract Full Text Full Text PDF PubMed Scopus (176) Google Scholar, M.A. Roos-Mattjus P.M. Rauen M. Babendure J.R. Karnitz L.M. J. Biol. Chem. 2001; 276: 25903-25909Abstract Full Text Full Text PDF PubMed Scopus (116) Google the C terminus of hRad9 as a regulatory for of this the of other of hRad9 such as Although we have identified two distinct forms of hRad9 phosphorylation, at sites of constitutive phosphorylation, and the of the and of hRad9 the of the constitutive sites of phosphorylation and the of for the and of In the cell cycle-regulated phosphorylation of hRad9 in G2 and through mitosis or are two In this is the first the hRad9 protein to the G2/M a in which the S. pombe protein an regulatory the that hRad9 undergoes at two distinct phosphorylation in response to IR other is that hRad9 hyper-phosphorylation in response to IR with with M.A. Karnitz L.M. J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Scopus Google and has to is an between two IR-induced phosphorylation of hRad9 with with DNA is an We and for We also and for and Lee and for the

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.