Inhibition of APCCdh1 Activity by Cdh1/Acm1/Bmh1 Ternary Complex Formation

The anaphase-promoting complex (APC) is an essential E3 ubiquitin ligase responsible for catalyzing proteolysis of key regulatory proteins in the cell cycle. Cdh1 is a co-activator of the APC aiding in the onset and maintenance of G1 phase, whereas phosphorylation of Cdh1 at the end of G1 phase by cyclin-dependent kinases assists in the inactivation of APCCdh1. Here, we suggest additional components are involved in the inactivation of APCCdh1 independent of Cdh1 phosphorylation. We have identified proteins known as Acm1 and Bmh1, which bind and form a ternary complex with Cdh1. The presence of phosphorylated Acm1 is critical for the ternary complex formation, and Acm1 is predominantly expressed in S phase when APCCdh1 is inactive. The assembly of the ternary complex inhibits ubiquitination of Clb2 in vitro by blocking the interaction of Cdh1 with Clb2. In vivo, lethality caused by overexpression of constitutively active Cdh1 is rescued by overexpression of Acm1. Partially phosphorylated Cdh1 in the absence of ACM1 still binds to and activates the APC. However, the addition of Acm1 decreases Clb2 ubiquitination when using either phosphorylated or nonphosphorylated Cdh1. Taken together, our results suggest an additional inactivation mechanism exists for APCCdh1 that is independent of Cdh1 phosphorylation. The anaphase-promoting complex (APC) is an essential E3 ubiquitin ligase responsible for catalyzing proteolysis of key regulatory proteins in the cell cycle. Cdh1 is a co-activator of the APC aiding in the onset and maintenance of G1 phase, whereas phosphorylation of Cdh1 at the end of G1 phase by cyclin-dependent kinases assists in the inactivation of APCCdh1. Here, we suggest additional components are involved in the inactivation of APCCdh1 independent of Cdh1 phosphorylation. We have identified proteins known as Acm1 and Bmh1, which bind and form a ternary complex with Cdh1. The presence of phosphorylated Acm1 is critical for the ternary complex formation, and Acm1 is predominantly expressed in S phase when APCCdh1 is inactive. The assembly of the ternary complex inhibits ubiquitination of Clb2 in vitro by blocking the interaction of Cdh1 with Clb2. In vivo, lethality caused by overexpression of constitutively active Cdh1 is rescued by overexpression of Acm1. Partially phosphorylated Cdh1 in the absence of ACM1 still binds to and activates the APC. However, the addition of Acm1 decreases Clb2 ubiquitination when using either phosphorylated or nonphosphorylated Cdh1. Taken together, our results suggest an additional inactivation mechanism exists for APCCdh1 that is independent of Cdh1 phosphorylation. The eukaryotic cell cycle is largely controlled by targeted proteolysis of regulatory proteins, specifically through ubiquitin-mediated proteolysis (1Michalides R.J. van de Brekel M. Balm F. Head Neck. 2002; 24: 694-704Crossref PubMed Scopus (22) Google Scholar, 2McDonald 3rd, E.R. El-Deiry W.S. Ann. Med. 2001; 33: 113-122Crossref PubMed Scopus (51) Google Scholar, 3Yam C.H. Fung T.K. Poon R.Y. Cell Mol. Life Sci. 2002; 59: 1317-1326Crossref PubMed Scopus (392) Google Scholar, 4Pray T.R. Parlati F. Huang J. Wong B.R. Payan D.G. Bennett M.K. Issakani S.D. Molineaux S. Demo S.D. Drug Resist. Updat. 2002; 5: 249-258Crossref PubMed Scopus (57) Google Scholar). The anaphase-promoting complex (APC) 2The abbreviations used are: APC, anaphase-promoting complex; E2, ubiquitin carrier protein; E3, ubiquitin-protein isopeptide ligase; CDK, cyclin-dependent kinase; CAB complex, complex of Cdh1 Acm1 and Bmh1; GST, glutathione S-transferase; Bis-Tris, 2-bis(2-hydroxyethyl)amino-2-(hydroxymethyl)propane-1,3-diol; TOF, time-of-flight; WT, wild type; FACS, fluorescence-activated cell sorting. is an essential E3 ubiquitin ligase responsible for catalyzing proteolysis of key regulatory proteins in the cell cycle. Substrate specificity of the APC is attributed to co-activator proteins that associate with particular substrates throughout the cell cycle (5Kramer E.R. Gieffers C. Holzl G. Hengstschlager M. Peters J.M. Curr. Biol. 1998; 8: 1207-1210Abstract Full Text Full Text PDF PubMed Google Scholar, 6Schwab M. Neutzner M. Mocker D. Seufert W. EMBO J. 2001; 20: 5165-5175Crossref PubMed Scopus (167) Google Scholar, 7Visintin R. Prinz S. Amon A. Science. 1997; 278: 460-463Crossref PubMed Scopus (720) Google Scholar). The co-activators Cdc20 and Cdh1 are thought to aid in the recruitment of particular substrates through substrate binding independent of the APC or in assemblies known as APCCdc20 or APCCdh1 (8Eytan E. Moshe Y. Braunstein I. Hershko A. Proc. Natl. Acad. Sci. U. S. A. 2006; 103: 2081-2086Crossref PubMed Scopus (53) Google Scholar, 9Kraft C. Vodermaier H.C. Maurer-Stroh S. Eisenhaber F. Peters J.M. Mol. Cell. 2005; 18: 543-553Abstract Full Text Full Text PDF PubMed Scopus (181) Google Scholar, 10Passmore L.A. Barford D. EMBO Rep. 2005; 6: 873-878Crossref PubMed Scopus (45) Google Scholar). The APC polyubiquitinates substrates, marking them for degradation by the proteasome (6Schwab M. Neutzner M. Mocker D. Seufert W. EMBO J. 2001; 20: 5165-5175Crossref PubMed Scopus (167) Google Scholar, 11Pfleger C.M. Lee E. Kirschner M.W. Genes Dev. 2001; 15: 2396-2407Crossref PubMed Scopus (203) Google Scholar). Ubiquitin ligase activity of the APC has been shown to require the presence of Cdc20 or Cdh1 (5Kramer E.R. Gieffers C. Holzl G. Hengstschlager M. Peters J.M. Curr. Biol. 1998; 8: 1207-1210Abstract Full Text Full Text PDF PubMed Google Scholar, 11Pfleger C.M. Lee E. Kirschner M.W. Genes Dev. 2001; 15: 2396-2407Crossref PubMed Scopus (203) Google Scholar, 12Fang G. Yu H. Kirschner M.W. Mol. Cell. 1998; 2: 163-171Abstract Full Text Full Text PDF PubMed Scopus (425) Google Scholar, 13Kramer E.R. Scheuringer N. Podtelejnikov A.V. Mann M. Peters J.M. Mol. Biol. Cell. 2000; 11: 1555-1569Crossref PubMed Scopus (360) Google Scholar, 14Burton J.L. Solomon M.J. Genes Dev. 2001; 15: 2381-2395Crossref PubMed Scopus (149) Google Scholar). Co-activators interact with the APC at specific times during the cell cycle, with Cdc20 activating the APC from early to late M phase and Cdh1 activating the APC from late M phase through G1 (5Kramer E.R. Gieffers C. Holzl G. Hengstschlager M. Peters J.M. Curr. Biol. 1998; 8: 1207-1210Abstract Full Text Full Text PDF PubMed Google Scholar, 12Fang G. Yu H. Kirschner M.W. Mol. Cell. 1998; 2: 163-171Abstract Full Text Full Text PDF PubMed Scopus (425) Google Scholar, 15Huang J.N. Park I. Ellingson E. Littlepage L.E. Pellman D. J. Cell Biol. 2001; 154: 85-94Crossref PubMed Scopus (93) Google Scholar). Phosphorylation of Cdh1 has been demonstrated as an important control mechanism for the APCCdh1 complex (16Zachariae W. Schwab M. Nasmyth K. Seufert W. Science. 1998; 282: 1721-1724Crossref PubMed Scopus (442) Google Scholar). Phosphorylation of Cdh1 is cell cycle-dependent and is considered to be the main regulatory mechanism by which APCCdh1 is inactivated. Cdh1 is phosphorylated in S phase, G2, and mitosis and dephosphorylated in G1 (16Zachariae W. Schwab M. Nasmyth K. Seufert W. Science. 1998; 282: 1721-1724Crossref PubMed Scopus (442) Google Scholar). The phosphorylation of Cdh1 corresponds to high levels of the cyclin-dependent kinase (CDK) activity. When the CDK consensus phosphorylation sites within Cdh1 from budding yeast were mutated to alanine, Cdh1 activated the APC constitutively, failing to accumulate mitotic cyclins (16Zachariae W. Schwab M. Nasmyth K. Seufert W. Science. 1998; 282: 1721-1724Crossref PubMed Scopus (442) Google Scholar). Cdh1 is phosphorylated at the G1/S phase transition by G1 and S phase cyclins that activate the CDK in budding yeast, Cdc28. Cdh1 remains hyperphosphorylated until late in mitosis when Cdc14 phosphatase is activated allowing Cdh1 to reactivate the APC (15Huang J.N. Park I. Ellingson E. Littlepage L.E. Pellman D. J. Cell Biol. 2001; 154: 85-94Crossref PubMed Scopus (93) Google Scholar, 17Prinz S. Hwang E.S. Visintin R. Amon A. Curr. Biol. 1998; 8: 750-760Abstract Full Text Full Text PDF PubMed Scopus (189) Google Scholar). In S and M phases, Cdh1 failed to associate with the APC in Cdh1 co-immunoprecipitations (16Zachariae W. Schwab M. Nasmyth K. Seufert W. Science. 1998; 282: 1721-1724Crossref PubMed Scopus (442) Google Scholar). Additionally, in vitro phosphorylation of recombinant Cdh1 by CDKs is sufficient for inactivation of the APC (18Jaspersen S.L. Charles J.F. Morgan D.O. Curr. Biol. 1999; 9: 227-236Abstract Full Text Full Text PDF PubMed Scopus (346) Google Scholar). Protein-protein interactions have also been shown to be important in the regulation of Cdh1 (19Reimann J.D. Gardner B.E. Margottin-Goguet F. Genes Dev. 2001; 15: PubMed Scopus Google Scholar, J. G. Genes Dev. 2001; 15: PubMed Scopus Google Scholar). In and have been shown to Cdh1 through interactions (19Reimann J.D. Gardner B.E. Margottin-Goguet F. Genes Dev. 2001; 15: PubMed Scopus Google Scholar, J. G. Genes Dev. 2001; 15: PubMed Scopus Google Scholar). the of is is to substrate binding to Cdh1. However, in yeast have been Cdh1 proteins, we a of Cdh1 in budding In the we identified a complex that with of a Acm1 and of the known as and The of Acm1 is cell and Acm1 is for complex with Cdh1 and of the complex, which we to as the CAB complex or complex, is to the cell cycle in which Acm1 is Clb2 levels in when with Acm1 inhibits APCCdh1 activity in and lethality caused by overexpression of constitutively active Cdh1 is rescued by Acm1 The CAB complex to substrate binding with the Partially phosphorylated Cdh1 binds and activates the APC in the absence of Acm1. we have shown the of Acm1 and to APCCdh1 the Cdh1 phosphorylation Taken together, our suggest the of an additional inactivation mechanism of APCCdh1 independent of Cdh1 phosphorylation. for and have been C.H. Cell PubMed Scopus Google Scholar). The constitutively from the the with of CDK sites mutated to from the The from from the and from the were from M. The and were from D. Barford L.A. A. Barford D. EMBO J. PubMed Scopus Google Scholar). and were by from yeast and at the and sites a the of and Clb2 for overexpression in were by and are in were yeast yeast and yeast or used in C.H. J. Biol. 278: Full Text Full Text PDF PubMed Scopus Google in a Cell G1 in is to the during phase at require for an G1 in S phase the addition of M phase are by the addition of has a yeast that cell cycle in by from to Cell cycle are by until of the have the Cdh1 were to and in of and by for at in of Cell by at for were and a at for were with for at Cdh1 with and with in APC were and and were in the as for Cdh1. from were with for at in from were to at and to for from were with for at with and with in Acm1 were and and were in the as for Cdh1 from were with for at in Acm1 to used in binding Acm1 used in the ubiquitination and Clb2 binding with for at at to the at a of used in the ubiquitination and binding in the as APC. of E. or in the were and used to of yeast were for at to and were and by The cell in were using for with a were by at and for were with of for and were and to were with of used the for binding used in the ubiquitination with to the The with to with using with a In were used for binding used as and in the used as to and to for times at were with of and in the used the In used for of the were as by D. Barford L.A. A. Barford D. EMBO J. PubMed Scopus Google Scholar). The substrate Clb2 the co-activator Cdh1 and the were using the in vitro APC and Acm1 were from budding yeast APC and Acm1 whereas expressed and from E. APC used in of the from of Clb2 with Life were a and using were as C.H. J. Biol. 278: Full Text Full Text PDF PubMed Scopus Google Scholar). a and used to of and and from Cdh1 were in and a were with or were and with were and in a of were a and proteins were identified using the that were a C.H. Mol. Biol. 2005; Google Scholar). were from S in The were a with an at were in and were by and by with an Acm1 and with Cdh1 in and in and a proteins of we used a targeted of with Cdh1 by We proteins known as Bmh1, and in budding yeast, which interact with Cdh1 high The used as a Cdh1 were also identified by we specific proteins in the Cdh1 to the high which the of the complex of Cdh1 and Acm1 in a interaction Acm1 is a with known identified as a CDK substrate M. J.D. K. Morgan D.O. PubMed Scopus Google Scholar). However, as of the of proteins, and have been with a of and have been as proteins Cell. Full Text Full Text PDF PubMed Scopus Google Scholar, H. Cell. 2000; PubMed Scopus Google Scholar). We for interactions either as APCCdh1 substrates or as of Cdh1. the specificity of the interactions and Bmh1, we used in vitro binding Cdh1 and Acm1 were from yeast recombinant expressed in E. and with to used as a and with as a with We interactions and Acm1 and and Acm1 and high of the CAB complex for complex formation, we from for components of the We expressed Cdh1 in WT, and and with by and for Bmh1, and were and be in the absence of Acm1. In the Acm1 and still with Cdh1. Acm1 and still with Cdh1 in the Additionally, we from either or with in an in vitro binding Cdh1 bind The binding in is attributed to the presence of which with Cdh1. the of the CAB complex Acm1 as as a and Acm1 in S and an Cell Cdh1 activates the APC in a cell cycle-dependent the interaction with Acm1 and the proteins also throughout the cell cycle. proteins were in a cell cycle-dependent and levels were in cell from and M Acm1 levels were to be in S phase the cell cycle phases, whereas levels in cell cycle is in with the Acm1 throughout the cell cycle G. K. D. Mol. Biol. Cell. 1998; 9: PubMed Scopus Google Scholar). of Acm1 levels from the the of to Acm1 is for G. K. D. Mol. Biol. Cell. 1998; 9: PubMed Scopus Google Scholar). is to be the complex responsible for phosphorylation of Cdh1 during S phase, G1 are also involved (15Huang J.N. Park I. Ellingson E. Littlepage L.E. Pellman D. J. Cell Biol. 2001; 154: 85-94Crossref PubMed Scopus (93) Google Scholar, A. S. Nasmyth K. Cell. Full Text PDF PubMed Scopus Google Scholar, Y. U. Mol. Cell. Biol. 2001; PubMed Scopus Google Scholar). Acm1 levels are in S phase when Cdh1 is phosphorylated and APCCdh1 inactivated. an of Acm1 in regulation of APCCdh1 during S We the of ACM1 to in the cell cycle. to the with ACM1 were G. C. S. S. A. K. A. M. R. R. S. S. M. K. A. F. M. D. U. S. S.L. D. N. H. H. C. M. R. S.L. J.L. M. G. S. J.N. G. M. G. T.R. J. Y. G. E. Yu K. H. J.D. M. M. 2002; PubMed Scopus Google Scholar). at when with ACM1 within a cell cycle, from and were in S phase with and by for in of an in the S phase cell in to at to Additionally, the with in M The in S phase in Acm1 a in cell cycle throughout S the CAB complex a in APCCdh1 a in APCCdh1 substrate levels in Acm1. APCCdh1 substrates are in we a G1 in Acm1 with of Acm1 and levels of the known APCCdh1 substrate Clb2. we a in Clb2 levels in early in the absence of Acm1 The of Clb2 corresponds to that of Acm1 to Clb2 of APCCdh1 activity in the Acm1 in Clb2 levels the However, the in the cell cycle are CAB complex as an mechanism in addition to phosphorylation for APCCdh1. CAB of Acm1 predominantly expressed in S phase when APCCdh1 activity is and Acm1 a in Clb2 we the CAB complex APCCdh1 activity a of Acm1 and APC an in vitro ubiquitination used to ubiquitination of the substrate Clb2 APC and Acm1 were from yeast and Clb2 were expressed in vitro and for the The of substrate ubiquitination by of Clb2. levels of in a of Clb2 ubiquitination from used to or APCCdh1 activity and Clb2 ubiquitination levels Acm1 to APC and Cdh1 we used yeast APC, and Acm1 Acm1 to APC activity at levels and we have binding from our We to the presence of a of Cdh1 in the Clb2 ubiquitination the addition of is to the of Acm1 for the our in vitro ubiquitination we Acm1 and have an APCCdh1 ubiquitin ligase activity. Acm1 inhibits APCCdh1 activity in vivo, we Acm1 and the constitutively active Cdh1 of the CDK phosphorylation sites mutated to has been shown that Cdh1 Cdh1 were to accumulate Clb2 and to form mitotic and (16Zachariae W. Schwab M. Nasmyth K. Seufert W. Science. 1998; 282: 1721-1724Crossref PubMed Scopus (442) Google Scholar). We overexpression of Acm1 the lethality caused by overexpression of the Cdh1 we the CAB complex APCCdh1 activity as an regulatory mechanism in the absence of CDK phosphorylation. mechanism exists in addition to Cdh1 which has been shown to also APCCdh1 activity. CAB complex to APCCdh1 of the phosphorylation of Cdh1. CAB complex APCCdh1 activity. activity of APCCdh1 is by the interaction APC, and the we the complex either APC binding to Cdh1 or Cdh1 binding to Clb2. Acm1 and were APCCdh1 activity by blocking the interaction or by blocking substrate binding to we binding and with or the presence of the complex components and expressed with from Cdh1 with levels of Acm1 in an in vitro binding In the in vitro binding from and and with APC in Cdh1 binding to the APC be in the presence or absence of Acm1 and Cdh1 binding to Clb2 in a with levels of Acm1 Acm1 the interaction the substrate and which CAB complex inhibits APCCdh1 activity. of the the important Cdh1 phosphorylation in the inactivation of APCCdh1 activity. we phosphorylation with the interaction and phosphorylation in the complex, we an in vitro binding and Cdh1 with and phosphatase of Cdh1 from with and with in an in vitro binding with phosphatase used as a in Cdh1 to be when a phosphatase Cdh1 with and However, Cdh1 from Acm1 is shown Acm1 is for the Acm1 of the consensus CDK and we have that Acm1 is phosphorylated in Cdh1 from we the of or in the binding of Cdh1 with phosphorylation of Cdh1 or Acm1 to of the complex, we from and from and with phosphatase in an in vitro binding we that phosphorylation is for the interaction Cdh1 and and the addition of Acm1 phosphorylation an in vitro binding with with or from of Acm1 binding to that phosphorylation of Acm1 Cdh1 is critical for the CAB complex and Cdh1 and the APC in and by Acm1 has the to lethality caused by constitutively active Cdh1 with of the CDK sites mutated to alanine, we phosphorylated Cdh1 still bind and activate the APC. we in phosphorylated Cdh1 still bind to the APC in the absence of the we Cdh1 to the APC in an in vitro binding and used phosphatase the complex to that Cdh1 to the APC is still from and with APC for at with the Cdh1 and and with were by and by We Cdh1 to the APC were a to phosphorylated from dephosphorylated Cdh1. to of Cdh1 be from and We the Cdh1 to the APC is phosphorylated to the that phosphorylated Cdh1 bind or activate the APC (16Zachariae W. Schwab M. Nasmyth K. Seufert W. Science. 1998; 282: 1721-1724Crossref PubMed Scopus (442) Google Scholar, S.L. Charles J.F. Morgan D.O. Curr. Biol. 1999; 9: 227-236Abstract Full Text Full Text PDF PubMed Scopus (346) Google Scholar). in phosphorylation of Cdh1 in the absence of the complex the interaction Cdh1 and the APC. phosphorylation of Cdh1 the interaction with the APC, we the phosphorylated co-activator activate the APC. the we Cdh1 phosphorylation a for the interaction with Acm1. we also the addition of Acm1 and Clb2 ubiquitination using phosphorylated or nonphosphorylated Cdh1. we Cdh1 from the for by and used phosphorylated and dephosphorylated Cdh1 in the in vitro ubiquitination Cdh1 to phosphatase to Cdh1 to the We of Cdh1 to of phosphorylated and dephosphorylated Cdh1 were sufficient for ubiquitin ligase activity and the addition of Acm1 and Bmh1, a in Clb2 ubiquitination be using and Cdh1 and Cdh1 phosphorylation is for Acm1 binding and Acm1 and as an early mechanism of phosphorylated Cdh1 the cyclin-dependent kinase Cdh1 for Acm1 and as an mechanism of the phosphorylation of Cdh1 to APC inactivation at the G1/S phase transition and during S has shown the phosphorylation of Cdh1 at the end of G1 phase by the cyclin-dependent kinase and has demonstrated that phosphorylation is responsible for the inactivation of the APCCdh1 complex (16Zachariae W. Schwab M. Nasmyth K. Seufert W. Science. 1998; 282: 1721-1724Crossref PubMed Scopus (442) Google Scholar, S.L. Charles J.F. Morgan D.O. Curr. Biol. 1999; 9: 227-236Abstract Full Text Full Text PDF PubMed Scopus (346) Google Scholar, M. Morgan D.O. 2005; PubMed Scopus Google Scholar). Cdh1 constitutively activate the APC from Clb2 and (16Zachariae W. Schwab M. Nasmyth K. Seufert W. Science. 1998; 282: 1721-1724Crossref PubMed Scopus (442) Google Scholar). Additionally, in vitro phosphorylation of recombinant Cdh1 is sufficient for inactivation of the APC (18Jaspersen S.L. Charles J.F. Morgan D.O. Curr. Biol. 1999; 9: 227-236Abstract Full Text Full Text PDF PubMed Scopus (346) Google Scholar). is phosphorylation of Cdh1 an important in APC the cell cycle a and inactivation of the APC Cdh1 has been shown to bind substrates independent of the APC C. Vodermaier H.C. Maurer-Stroh S. Eisenhaber F. Peters J.M. Mol. Cell. 2005; 18: 543-553Abstract Full Text Full Text PDF PubMed Scopus (181) Google Scholar, 14Burton J.L. Solomon M.J. Genes Dev. 2001; 15: 2381-2395Crossref PubMed Scopus (149) Google Scholar, J.L. Solomon M.J. Mol. Cell. 2005; 18: Full Text Full Text PDF PubMed Scopus Google for the regulation of Cdh1 be to the co-activator from with substrates during of the cell cycle is is that have inactivation to be are The remains for proteins to for APCCdh1 Here, we have identified an additional mechanism that of Cdh1 phosphorylation to Cdh1 from activating the APC. The mechanism is of complex of Acm1 and with Cdh1 and to APCCdh1 activity by blocking substrate binding to the The CAB complex is the APCCdh1 identified in Acm1 is the critical involved in complex and is cell the interaction is to the cell cycle during which Acm1 is We identified Bmh1, and as proteins using Cdh1 and to be and of is in with the of of the Cell. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, D. J. K. K. K. S. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). and are of the of proteins and as as of binding H. Cell. 2000; PubMed Scopus Google Scholar, M.J. van 2001; 18: PubMed Scopus Google Scholar). proteins have been as proteins with binding of Cell. Full Text Full Text PDF PubMed Scopus Google Scholar, K. S. A. H. Cell. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). The of the complex, which with is a that has been Acm1. Acm1 has been shown to interact with yeast T.R. S. M. J.D. C.H. B.E. S. D. 3rd, Mol. Cell. Full Text Full Text PDF PubMed Scopus Google Scholar). Acm1 has been identified as a substrate and CDK phosphorylation sites that the consensus M. J.D. K. Morgan D.O. PubMed Scopus Google Scholar). the of Acm1 is to that of is for Cdh1 phosphorylation and S phase we have of Acm1 in the remains an exists or that proteins an Acm1 in of Cdh1 in a for S phase to The presence of Acm1 is at the specific when APCCdh1 to be inactivated. levels of Acm1 are in S phase with the phosphorylation of Cdh1 by of Acm1 a in the cell cycle to an of in S we the S phase is a of early S phase or through S Additionally, we have Clb2 levels in a G1 and an APCCdh1 activity in the absence of Acm1. The levels of Clb2 in early However, Clb2 levels to a at in the that we to of APCCdh1 by phosphorylation. The cell cycle be by Clb2 a S phase as a of CDK activity M.K. Mol. Cell. 1998; 2: Full Text Full Text PDF PubMed Scopus Google Scholar). However, our suggest Acm1 has regulatory during S are to levels of S phase cyclins in Phosphorylation of Cdh1 in S phase, and phosphorylation the binding Cdh1 and the APC. We have shown in phosphorylated Cdh1 binds to and activates the APC, be Cdh1 is We have demonstrated Acm1 and have a APCCdh1 activity in vitro and in and that by Acm1 and when Cdh1 is phosphorylated or the phosphorylation of Cdh1 CAB complex formation, phosphorylation of Acm1 a critical in the assembly of the ternary complex with and Cdh1. We have identified within Acm1 from Cdh1 is Acm1 identified as a substrate M. J.D. K. Morgan D.O. PubMed Scopus Google Scholar). of Acm1 has Cdh1 binding Phosphorylation of Acm1 and Cdh1 in by the kinase to complex We have also a in the of Acm1 is The be a of which a in Acm1 binds phosphorylated Acm1 and has by to Acm1 from early We are phosphorylation of Acm1 is for APCCdh1 and is involved in Acm1 We have the of Acm1 and as APC levels of Acm1 S phase when the APC is ACM1 S phase, the Acm1 to be to of APCCdh1. degradation by APCCdc20 to Acm1 until is for APCCdh1 The and the have been identified as degradation in APC substrates J.L. Solomon M.J. Genes Dev. 2001; 15: 2381-2395Crossref PubMed Scopus (149) Google whereas Acm1 at and at and a at APC substrates, levels are throughout the cell cycle, and levels Additionally, interact with Cdh1 Acm1 is is an APC However, is to the of to be the APCCdh1 in and the CAB complex in APCCdh1 activity in vitro and bind Cdh1 J.D. J. Cell Biol. 2002; PubMed Scopus Google Scholar). and Acm1 are during S phase and are during M phase J.D. E. E.R. Peters J.M. Cell. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). In a a has been as a of APCCdh1 and with substrates for Cdh1 binding M.K. A. Genes Dev. 2006; 20: PubMed Scopus Google Scholar). we have demonstrated Acm1 and binding Cdh1 and the APC substrate we have which in Acm1 are involved in Cdh1 binding or Acm1 an APC We have an interaction Acm1 and of Cdh1 in The of Cdh1 a shown to be the for substrate binding C. Vodermaier H.C. Maurer-Stroh S. Eisenhaber F. Peters J.M. Mol. Cell. 2005; 18: 543-553Abstract Full Text Full Text PDF PubMed Scopus (181) Google Scholar). We Acm1 also Cdh1 substrates to APCCdh1. the is and Acm1 of and is proteins the We are the mechanism of of the CAB complex in Cdh1 has been shown to from the to the from the of the APC phosphorylation as a mechanism M. van F. M. EMBO J. 2002; PubMed Scopus Google Scholar). proteins are involved in the of the cell cycle regulatory Acm1 and a with Cdh1 Y. H. Mol. Cell. Biol. 1999; PubMed Scopus Google Scholar, S. A. M. M. M. H. Y. K. J. Cell Sci. PubMed Scopus Google Scholar). However, the of Acm1 and Cdh1 has been additional for APC inactivation through interactions Lee Lee H. N. J. H. Kirschner M.W. Cell Biol. 6: PubMed Scopus Google Scholar, H. Curr. Cell Biol. 2002; PubMed Scopus Google Scholar). that the complex as an mechanism in addition to the phosphorylation to APCCdh1 activity to mitosis However, additional are to the and mechanism by which CAB complex inhibits APCCdh1. We M. and D. Barford for C. for and for the and Clb2 to H. J. and for critical the