- Email: [email protected]
Completing the next phase of the cycle: Kyoto to Cambridge
MISCELLANEA
The sake cups and chem] blossom ;arties of Kyoto two and a half years ago I Were exchanged for punt poles and umbrellas at St John's College, Cambridge for the Second UK-Japan Cell Cycle Workshop*. These workshops have formed the hub of a sedes of UK-lapan interactions over the past three years. The long-term success of the programme can be judged by the fact that this conference saw more than 50 Japanese delegates in Cambddge, ten of whom are now resident in UK labs. Indeed, discussions adsing at the first meeting led to the movement of one entire research team from Japan to the UK. In addition to such long-term migrations, numerous research exchanges have punctuated the natural liaison between two countries that excel in the field of cell cycle research. This excellence was reflected in the quality of the presentations, discussions and posters at the Cambridge workshop, which broke new ground in virtually evenj sphere of cell cycle research. A few of these exciting developments are descdbed here. Licensing factor Several years ago Ron Laskey (University of Cambridge, UK) and lullan Blow (now of ICRF, Clare Hall, UK) proposed that the crucial limitation of DNA replication to one complete round per cell cycle is a conseQuence of DNA being 'licensed' by a factor late one cell cycle to be replication competent in the nexta, Blow and Laskey speculated that specific cellular localization played a key role in licensing. Working on the assumption that 'licensing factor' would show cell-cyclespecific association with chromatin, Haruhiko Taklsawa (Osaka University, lapan) used Xenopus oocyte extracts to purify potential licensing factor components, and succeeded in cloning one of them, pl00, from both frog and human. Perhaps not surprisingly, nucleotide sequencing of the pl00 gene predicted that it encodes a mere. ber of the 'CDC46/MCM' family, most closely related to MCM3. Proteins of the CDC46/MCM family (MCM stands for minichromosome maintenance) are essential for the initiation of DNA replication in yeast and have received much attention as potential candidates for licensing factor components 3,4. Using different approaches, but again in Xenopus, Blow and Laskey also independently arrived at the conclusion that pf 00 is essential for licens. ing activity. Moreover, they indicated that although pl00 fulfils the criteria
Completing the next phase of the cycle: Kyoto to Cambridge Takashi Toda and lain Hagan required of an active component of the licensing factor, on its own it is not suflident for activity; Blow pointed out that additional factors for DNA-binding and ATP-hydrolysing activities are important, while Laskey showed that nuclear localization of pl00 is not sufficient to license DNA for replication.
Initiation of S phase Using a sensitive in vivofootprinting technique, John Diffley (ICRF, Clare Hall) identified a difference in hypersensitive sites and protection patterns in the replication origin tARS) of pre. and post-replication chromatin s'e. Diffley further suggested that DBF4, which Is a regulator of the CDC7 protein klnase9, interacts with the originrecognition complex (ORC). KIm Nasmyth (Research institute of Molecular Pathology, Vienna, Austria) presented elegant work on p40 srrt, which he proposed to be an inhibitor of the CLB$,6-CDC28 klnase, p4051cJ, originally identified as a substrate of the CDC28 kinase and later shown to inhibit its activity specificallyl°,n, belongs to a growing family of CDK In. hlbitors that regulate the G 1-S transition. Interestingly, p40 slcl may be downstream or even a direct target of CDC34, a ubiquitin.conjugating enzyme12,because a temperature-sensitive cdc34 mutant, which usually arrests cell cycle progression in G1 phase, can execuLe S phase if $tC1 is deleted in cdc34 mutant cells. Nasmyth also reported the isolation of a series of mutants that specifically bypass the block to DNA replication caused by loss of function of members of the cyclin-B-like CLB gene family, and thus allow endoreplication without inteivening mitosis in the temperature.sensitive single clb2 and triple clbl;clb3;db4 disruption background. Thus, the notion that diverse functions of the cdc2/CDC28 kinase dudl~g distinct stages of the cell cycle are performed by associationdissociation of different partners of
TRENDS IN CELL BIOLOGYVOL. 4 DECEMBER1994
cyclin subunits13and also possibly different CDK/cyclin inhibitors is gaining overwhelming credence. Coordinating $ phase and M phase CDK inhibitors were again in the spotlight of discussions of the key issue as to how the cycle is coordinated into successive S and M phases. Among several points raised by Paul Nurse (ICRF, Lincoln's Inn Fields, UK) was the suggestion that in fission yeast mitosis is held in check during G1 phase by a physical interaction between the rum1 and cdcl 3 (a B-type cyclin) proteins, rumt was originally isolated by Moreno and Nurse as a gene whose ectopic overexpression caused multiple rounds of S phase without mitoses and whose deletion abolished the G1 phase of the cell cycle (thus abolishing the window of the cycle during which cells can conjugate and making the strains sterile) TM, Antibodies against rum1 were found to coprecipitate cdcl 3 but not p34cdc2;thus rum1 may inhibit mitosis by binding to cdc13 and abolishing its interaction with p34 ~4ca,Consistent with this involve. merit of cdcl 3 in mitotic regulation, lacky Hayles (ICRF, Lincoln's Inn Fields) demon:;treted that deletion of the cdcl3 gene leads to multiple rounds of S phase without any mitoses is. Manipulation of rural is not only revealing S-M links but, according to Sergio Moreno (Institute de Microbiologia Bioquimica, Salamanca, Spain), is also proving a useful tool in the analysis of the elusive controls r~lulating G1 progression in fission yeasL. In a senes ot genetic tests he showed that manipulation of cigl, cig2 and pucl, which encode cyclin homologues, could restore a G1 phase and mating proficiency to rural- mutants. Thus, understanding which G1 and G2 cyclins associatewith the cdc2 cata. lyric subunit and how this interaction is regulated could well be a key to understanding the temporal dependency of S and M phase. Cell cycle regulation and transcriptllon Approaches to the cell cycle problem from the field of oncogenesis were
© ! 994 ElsevierScienceLtd 0962-89241941507.00
*The Second UK-JapanCell CycleWorkshop. Organizedby the UK and Japanese Cell CycleGroups [convenedby leremy Hyams (University CollegeLondon) and Mitsuhiro Yangadia(Kyoto University,Japan), respectively]with the pdmary support of the Bdtbh Council, RoyalSociety, Japan Societyfor the Promotionof Science,and Ministnj of Education, Scienceand Cultureof Japan. Cambridge, UK; 17-20 September 1994.
TakashiTodais at the Laboraton/of Cell Regulation, Imperial Cancer ResearchFund, 44 Lincoln'sInn Fields,LondonUK WCT~ 3PX,and is a member of the Dept of Biophysics,Faculty of Science,Kyoto University,Sakyoku, Kyoto 606-01 lapan; lain Hagan is at the Schoolof Biological Sciences,2.205 Stopford Building, Manchester University,Oxford Road, Manchester, UK MI39PT. 437
|lllINflllmmmzlj~j
~
under represented at the meeting, but Nic Jones (ICRF, Lincoln's Inn Fields) illustrated the powerful contribution to understanding cell cycle regulation that such an aporoach can give, in reporting his group's observations on the phosphorylation of the transcripUon factor E2F1. E2F positively regulates the expression of a number of genes involved in DNA replication. F.2F1is inactivated by a physical association with the retinoblastoma protein (pRb) and, upon infection by adenovirus, E1A binds to pRb and E4 binds to E2F1, leading to dissociation and activation of F.2F1.Jones showed that two sites on E2F1 were phosphorylated in a signal.dependent manner and that phosphorylation both prevented an interaction with pRb and was a prerequisite for interaction with E4TM. Cyclin-D1/D2-CDK2/4 but no~.cydinE-CDK2 complexes could carry out such phosphorylation. Through his analysis of transcriptional regulation in budding yeast, Lee Johnston (NIMR, Mill Hill, UK) cloned a novel gene, BRY1, that encodes a protein simitar to bacterial response regulators. Multlcopy BRY1 suppresses lethal double disruptions of any combination of the genes encoding the transcription factors $Wl4, SWI6 and MBP11z indicating the exciting possibility that two.component system signal transductlon may function in the regulation of DNA synthesis,
Undoing the work of the klnoaes While much attention has focused on the effects of kinases, other groups have been diverting their attention into studying the phosphatases that are responsible for cell cycle regulation. As with kinases, the identification of regulatory subunits and any clues as to how these may be targeted are much sought after. In this context, the presentation of Mitsuhiro Yanagida (Kyoto University, Japan)was particularly informative as he showed that the product of the disl gene, which genetically interacts with protein phosphatase 2A, associatesspecifically with cytoplasmic but not spindle microtubules. Interestingly, dis1- mutants and mutations in the gene encoding the PP1 catalytic subunit (the dis2 gene) have similar phenotypes of defects in chromosome segregation and completion of mitosis le,19. Cell cycle and the nucleus RCC1,originallyidentified asthe product of a clleckpoint gene whose mutation causespremature chromosome 438
MISCELLANEA
condensati-~i without completion of S phase2°, is now known to be a key molecule in nuclear dynamics, structure and transport. RCC1 has a GDP-GTP exchange activity for the nuclear GTPbinding protein Ran/TC4zl. Takeharu Nishimoto (Kyushu University, Japan) has identified, using the yeast twohybrid screening system, two Raninteracting proteins. One of them, RanBP1zz, seems to work antagonistically with RCC1 as it inhibits the release of GDP from Ran. The other, RanBP2, is a large protein of 300 kDa. The protein is complex but contains interesting features, including zinc finger motifs, four repeating structures found in a number of nuclear pore proteins and a cyclophilin-homology motif. The RCC1-Ran story is becoming increasingly complicated and it may be some time before we understand the molecular function of these fascinating molecules.
Effectors As with most meetings on the cell cycle, attention was not solely focused on how transitions are regulated but also on how the physical events that are being regulated are achieved. One event that occurs upon the G2-M transition is a change in microtubule dynamics mediated by mlcrotubule. severing factors. Elsuke Nishlda (institute for Virus Research, Kyoto, Japan)reported tile Isolation of a novel mlcrotubule-severlng factor from Xenopus M phase extracts that Is identical to elongation factor lcz. Interest. ingly, this protein has previously been localized to the spindle apparatus and the mlcrotubule.organlzing centre=s'ae. Friendship and the future Despite the geographical separation of the cell cycle research communities in the UK and Japan, it was clear from the meeting that there is considerable complementation of interests, approaches and skills and that both groups will benefit if meetings such as this can be held at similar intervals in the future, In his concluding remarks, Professor Yanagida highlighted one aspect of this complementation, by contrasting the long history of achievement in British science, ranging from Newton and Darwin through Watson and Crick to the present, with the 120-year history of Japanese scientific endearour since the Meiji Restoration. He particularly encouraged younger Japanese scientists to learn from the interchange. The Brit;sh were left pondering, in this respect, that given
the balance of presentations at this meeting they will soon be outstripped. References 1 HAGAN,I. andTODA,T. (1992) Trends Cell Biol. 2, 245-246 2 BLOW,I. ]. and LASKEY,R.A. (1988) Nature 332,546-548 3 HENNESSY,K. M., CIJ~K,C. D. and BOTSTEIN,D. (1990)GenesDev. 4, 2252-2263 4 ~ B-K.(i,994)TrendsCelIBiol.4,160-166 5 BELL,S.P.andSTILLMAN,B. (1992) Nature 128-.134 6 DIFFLEY,I- F.X. andCOCKER,I. H. (1992) Nature 357,169-172 7 BELLS.P.,KOBAYASHI,R.andSTIUMAN,B. (1993)Sdence262, 1844-1849 8 MICKLEM,G., ROWLEY,A., HARWOOD,I., NASMYTH,K. andDIFFLEY,). F. X. (~993) Nature 366,87-89 9 JOHNSTON,L. H. (1992)Trends CellBioL 2, 353-357 10 NUGROHO,T. T.and MENDENHALL,M. D. (1994)Mol. Cell. Biol. 14, 3320-3328 11 DONOVAN,I. D., TOYN,I. H., JOHNSTON,A. L. andJOHNSTON,L. H. (1994) GenesDev. 8, 1640-1653 12 GOEBLE,M. G.,YOCHEM,J., IENTSCH,S., MCGRATH,I. P.,VARSHAVSKY,A. and BYERS,B. (1988)Science241, 1331-1335 13 NASMY'I"H,K. (1993)Curt.Opin. CellBiol. S, 166-179 14 MORENO,S.andNURSE,P. (1994) Nature 367,236-242 15 HAYLES,J,, FISHER,D., WOOLtARD,A, and NURSE,P.(1994)Cell 78, 813422 16 FAGAN,R., FLINT,K, l. andJONES,N, (1994) Cd178,799,-811 17 ANDREWS,8, 8. and MASON,$. W, (1993) Sdence261, 1S43-1544 18 OHKURA,H., ADACHI,Y.,KINOSHITA,N,, NIWA,O., TODA,1".andYANAGIDA,M. (1988) EMBO I, 7, 1465-1473 19 OHKURA,H.,KINOSHITA,N., MiYATANI,S., TODA,T. andYANAGIDA,M. (1989)Ce// 57, 997-1007 20 NISHIMOTO,T., ELLEN,E,and BA$CILICO,C, (1978)Ce//15,475-483 21 DASSO,M, (1993) rreeds81ochem.Sci. 18, 96-101 22 COUTAVAS,E.,REN,M,, OPPENHEIM,J.D., D'EUSTACHIO,P.andRUSH,M. G. (1993)Nature 366,585-587 23 KURIYAMA,R,and8ORISY,G. G. (1985) /. CettBtcg.'101,524-530 24 TORIYAMA,M., OHTA,K., ENDO,S.and SAKAI,H. (1988)Cell MotiL Cytoskel.9, 117-128 25 KURIYAMA,R.,SAVERIDGF.,P,, LEFEBVRE,P, and DASGUPTA,S.(1990)I. Cell ScL95, 231-236 26 OHTAK., TORIYAMA,M., MIYAZAKI,M., MUROFUSHI,H., HOSODA,S., ENDO,S. and SAKAI,H. (1990)./.Biol. Chem. 265, 3240-3247
TRENDSIN CELLBIOLOGYVOL. 4 DECEMBER1994
The sake cups and chem] blossom ;arties of Kyoto two and a half years ago I Were exchanged for punt poles and umbrellas at St John's College, Cambridge for the Second UK-Japan Cell Cycle Workshop*. These workshops have formed the hub of a sedes of UK-lapan interactions over the past three years. The long-term success of the programme can be judged by the fact that this conference saw more than 50 Japanese delegates in Cambddge, ten of whom are now resident in UK labs. Indeed, discussions adsing at the first meeting led to the movement of one entire research team from Japan to the UK. In addition to such long-term migrations, numerous research exchanges have punctuated the natural liaison between two countries that excel in the field of cell cycle research. This excellence was reflected in the quality of the presentations, discussions and posters at the Cambridge workshop, which broke new ground in virtually evenj sphere of cell cycle research. A few of these exciting developments are descdbed here. Licensing factor Several years ago Ron Laskey (University of Cambridge, UK) and lullan Blow (now of ICRF, Clare Hall, UK) proposed that the crucial limitation of DNA replication to one complete round per cell cycle is a conseQuence of DNA being 'licensed' by a factor late one cell cycle to be replication competent in the nexta, Blow and Laskey speculated that specific cellular localization played a key role in licensing. Working on the assumption that 'licensing factor' would show cell-cyclespecific association with chromatin, Haruhiko Taklsawa (Osaka University, lapan) used Xenopus oocyte extracts to purify potential licensing factor components, and succeeded in cloning one of them, pl00, from both frog and human. Perhaps not surprisingly, nucleotide sequencing of the pl00 gene predicted that it encodes a mere. ber of the 'CDC46/MCM' family, most closely related to MCM3. Proteins of the CDC46/MCM family (MCM stands for minichromosome maintenance) are essential for the initiation of DNA replication in yeast and have received much attention as potential candidates for licensing factor components 3,4. Using different approaches, but again in Xenopus, Blow and Laskey also independently arrived at the conclusion that pf 00 is essential for licens. ing activity. Moreover, they indicated that although pl00 fulfils the criteria
Completing the next phase of the cycle: Kyoto to Cambridge Takashi Toda and lain Hagan required of an active component of the licensing factor, on its own it is not suflident for activity; Blow pointed out that additional factors for DNA-binding and ATP-hydrolysing activities are important, while Laskey showed that nuclear localization of pl00 is not sufficient to license DNA for replication.
Initiation of S phase Using a sensitive in vivofootprinting technique, John Diffley (ICRF, Clare Hall) identified a difference in hypersensitive sites and protection patterns in the replication origin tARS) of pre. and post-replication chromatin s'e. Diffley further suggested that DBF4, which Is a regulator of the CDC7 protein klnase9, interacts with the originrecognition complex (ORC). KIm Nasmyth (Research institute of Molecular Pathology, Vienna, Austria) presented elegant work on p40 srrt, which he proposed to be an inhibitor of the CLB$,6-CDC28 klnase, p4051cJ, originally identified as a substrate of the CDC28 kinase and later shown to inhibit its activity specificallyl°,n, belongs to a growing family of CDK In. hlbitors that regulate the G 1-S transition. Interestingly, p40 slcl may be downstream or even a direct target of CDC34, a ubiquitin.conjugating enzyme12,because a temperature-sensitive cdc34 mutant, which usually arrests cell cycle progression in G1 phase, can execuLe S phase if $tC1 is deleted in cdc34 mutant cells. Nasmyth also reported the isolation of a series of mutants that specifically bypass the block to DNA replication caused by loss of function of members of the cyclin-B-like CLB gene family, and thus allow endoreplication without inteivening mitosis in the temperature.sensitive single clb2 and triple clbl;clb3;db4 disruption background. Thus, the notion that diverse functions of the cdc2/CDC28 kinase dudl~g distinct stages of the cell cycle are performed by associationdissociation of different partners of
TRENDS IN CELL BIOLOGYVOL. 4 DECEMBER1994
cyclin subunits13and also possibly different CDK/cyclin inhibitors is gaining overwhelming credence. Coordinating $ phase and M phase CDK inhibitors were again in the spotlight of discussions of the key issue as to how the cycle is coordinated into successive S and M phases. Among several points raised by Paul Nurse (ICRF, Lincoln's Inn Fields, UK) was the suggestion that in fission yeast mitosis is held in check during G1 phase by a physical interaction between the rum1 and cdcl 3 (a B-type cyclin) proteins, rumt was originally isolated by Moreno and Nurse as a gene whose ectopic overexpression caused multiple rounds of S phase without mitoses and whose deletion abolished the G1 phase of the cell cycle (thus abolishing the window of the cycle during which cells can conjugate and making the strains sterile) TM, Antibodies against rum1 were found to coprecipitate cdcl 3 but not p34cdc2;thus rum1 may inhibit mitosis by binding to cdc13 and abolishing its interaction with p34 ~4ca,Consistent with this involve. merit of cdcl 3 in mitotic regulation, lacky Hayles (ICRF, Lincoln's Inn Fields) demon:;treted that deletion of the cdcl3 gene leads to multiple rounds of S phase without any mitoses is. Manipulation of rural is not only revealing S-M links but, according to Sergio Moreno (Institute de Microbiologia Bioquimica, Salamanca, Spain), is also proving a useful tool in the analysis of the elusive controls r~lulating G1 progression in fission yeasL. In a senes ot genetic tests he showed that manipulation of cigl, cig2 and pucl, which encode cyclin homologues, could restore a G1 phase and mating proficiency to rural- mutants. Thus, understanding which G1 and G2 cyclins associatewith the cdc2 cata. lyric subunit and how this interaction is regulated could well be a key to understanding the temporal dependency of S and M phase. Cell cycle regulation and transcriptllon Approaches to the cell cycle problem from the field of oncogenesis were
© ! 994 ElsevierScienceLtd 0962-89241941507.00
*The Second UK-JapanCell CycleWorkshop. Organizedby the UK and Japanese Cell CycleGroups [convenedby leremy Hyams (University CollegeLondon) and Mitsuhiro Yangadia(Kyoto University,Japan), respectively]with the pdmary support of the Bdtbh Council, RoyalSociety, Japan Societyfor the Promotionof Science,and Ministnj of Education, Scienceand Cultureof Japan. Cambridge, UK; 17-20 September 1994.
TakashiTodais at the Laboraton/of Cell Regulation, Imperial Cancer ResearchFund, 44 Lincoln'sInn Fields,LondonUK WCT~ 3PX,and is a member of the Dept of Biophysics,Faculty of Science,Kyoto University,Sakyoku, Kyoto 606-01 lapan; lain Hagan is at the Schoolof Biological Sciences,2.205 Stopford Building, Manchester University,Oxford Road, Manchester, UK MI39PT. 437
|lllINflllmmmzlj~j
~
under represented at the meeting, but Nic Jones (ICRF, Lincoln's Inn Fields) illustrated the powerful contribution to understanding cell cycle regulation that such an aporoach can give, in reporting his group's observations on the phosphorylation of the transcripUon factor E2F1. E2F positively regulates the expression of a number of genes involved in DNA replication. F.2F1is inactivated by a physical association with the retinoblastoma protein (pRb) and, upon infection by adenovirus, E1A binds to pRb and E4 binds to E2F1, leading to dissociation and activation of F.2F1.Jones showed that two sites on E2F1 were phosphorylated in a signal.dependent manner and that phosphorylation both prevented an interaction with pRb and was a prerequisite for interaction with E4TM. Cyclin-D1/D2-CDK2/4 but no~.cydinE-CDK2 complexes could carry out such phosphorylation. Through his analysis of transcriptional regulation in budding yeast, Lee Johnston (NIMR, Mill Hill, UK) cloned a novel gene, BRY1, that encodes a protein simitar to bacterial response regulators. Multlcopy BRY1 suppresses lethal double disruptions of any combination of the genes encoding the transcription factors $Wl4, SWI6 and MBP11z indicating the exciting possibility that two.component system signal transductlon may function in the regulation of DNA synthesis,
Undoing the work of the klnoaes While much attention has focused on the effects of kinases, other groups have been diverting their attention into studying the phosphatases that are responsible for cell cycle regulation. As with kinases, the identification of regulatory subunits and any clues as to how these may be targeted are much sought after. In this context, the presentation of Mitsuhiro Yanagida (Kyoto University, Japan)was particularly informative as he showed that the product of the disl gene, which genetically interacts with protein phosphatase 2A, associatesspecifically with cytoplasmic but not spindle microtubules. Interestingly, dis1- mutants and mutations in the gene encoding the PP1 catalytic subunit (the dis2 gene) have similar phenotypes of defects in chromosome segregation and completion of mitosis le,19. Cell cycle and the nucleus RCC1,originallyidentified asthe product of a clleckpoint gene whose mutation causespremature chromosome 438
MISCELLANEA
condensati-~i without completion of S phase2°, is now known to be a key molecule in nuclear dynamics, structure and transport. RCC1 has a GDP-GTP exchange activity for the nuclear GTPbinding protein Ran/TC4zl. Takeharu Nishimoto (Kyushu University, Japan) has identified, using the yeast twohybrid screening system, two Raninteracting proteins. One of them, RanBP1zz, seems to work antagonistically with RCC1 as it inhibits the release of GDP from Ran. The other, RanBP2, is a large protein of 300 kDa. The protein is complex but contains interesting features, including zinc finger motifs, four repeating structures found in a number of nuclear pore proteins and a cyclophilin-homology motif. The RCC1-Ran story is becoming increasingly complicated and it may be some time before we understand the molecular function of these fascinating molecules.
Effectors As with most meetings on the cell cycle, attention was not solely focused on how transitions are regulated but also on how the physical events that are being regulated are achieved. One event that occurs upon the G2-M transition is a change in microtubule dynamics mediated by mlcrotubule. severing factors. Elsuke Nishlda (institute for Virus Research, Kyoto, Japan)reported tile Isolation of a novel mlcrotubule-severlng factor from Xenopus M phase extracts that Is identical to elongation factor lcz. Interest. ingly, this protein has previously been localized to the spindle apparatus and the mlcrotubule.organlzing centre=s'ae. Friendship and the future Despite the geographical separation of the cell cycle research communities in the UK and Japan, it was clear from the meeting that there is considerable complementation of interests, approaches and skills and that both groups will benefit if meetings such as this can be held at similar intervals in the future, In his concluding remarks, Professor Yanagida highlighted one aspect of this complementation, by contrasting the long history of achievement in British science, ranging from Newton and Darwin through Watson and Crick to the present, with the 120-year history of Japanese scientific endearour since the Meiji Restoration. He particularly encouraged younger Japanese scientists to learn from the interchange. The Brit;sh were left pondering, in this respect, that given
the balance of presentations at this meeting they will soon be outstripped. References 1 HAGAN,I. andTODA,T. (1992) Trends Cell Biol. 2, 245-246 2 BLOW,I. ]. and LASKEY,R.A. (1988) Nature 332,546-548 3 HENNESSY,K. M., CIJ~K,C. D. and BOTSTEIN,D. (1990)GenesDev. 4, 2252-2263 4 ~ B-K.(i,994)TrendsCelIBiol.4,160-166 5 BELL,S.P.andSTILLMAN,B. (1992) Nature 128-.134 6 DIFFLEY,I- F.X. andCOCKER,I. H. (1992) Nature 357,169-172 7 BELLS.P.,KOBAYASHI,R.andSTIUMAN,B. (1993)Sdence262, 1844-1849 8 MICKLEM,G., ROWLEY,A., HARWOOD,I., NASMYTH,K. andDIFFLEY,). F. X. (~993) Nature 366,87-89 9 JOHNSTON,L. H. (1992)Trends CellBioL 2, 353-357 10 NUGROHO,T. T.and MENDENHALL,M. D. (1994)Mol. Cell. Biol. 14, 3320-3328 11 DONOVAN,I. D., TOYN,I. H., JOHNSTON,A. L. andJOHNSTON,L. H. (1994) GenesDev. 8, 1640-1653 12 GOEBLE,M. G.,YOCHEM,J., IENTSCH,S., MCGRATH,I. P.,VARSHAVSKY,A. and BYERS,B. (1988)Science241, 1331-1335 13 NASMY'I"H,K. (1993)Curt.Opin. CellBiol. S, 166-179 14 MORENO,S.andNURSE,P. (1994) Nature 367,236-242 15 HAYLES,J,, FISHER,D., WOOLtARD,A, and NURSE,P.(1994)Cell 78, 813422 16 FAGAN,R., FLINT,K, l. andJONES,N, (1994) Cd178,799,-811 17 ANDREWS,8, 8. and MASON,$. W, (1993) Sdence261, 1S43-1544 18 OHKURA,H., ADACHI,Y.,KINOSHITA,N,, NIWA,O., TODA,1".andYANAGIDA,M. (1988) EMBO I, 7, 1465-1473 19 OHKURA,H.,KINOSHITA,N., MiYATANI,S., TODA,T. andYANAGIDA,M. (1989)Ce// 57, 997-1007 20 NISHIMOTO,T., ELLEN,E,and BA$CILICO,C, (1978)Ce//15,475-483 21 DASSO,M, (1993) rreeds81ochem.Sci. 18, 96-101 22 COUTAVAS,E.,REN,M,, OPPENHEIM,J.D., D'EUSTACHIO,P.andRUSH,M. G. (1993)Nature 366,585-587 23 KURIYAMA,R,and8ORISY,G. G. (1985) /. CettBtcg.'101,524-530 24 TORIYAMA,M., OHTA,K., ENDO,S.and SAKAI,H. (1988)Cell MotiL Cytoskel.9, 117-128 25 KURIYAMA,R.,SAVERIDGF.,P,, LEFEBVRE,P, and DASGUPTA,S.(1990)I. Cell ScL95, 231-236 26 OHTAK., TORIYAMA,M., MIYAZAKI,M., MUROFUSHI,H., HOSODA,S., ENDO,S. and SAKAI,H. (1990)./.Biol. Chem. 265, 3240-3247
TRENDSIN CELLBIOLOGYVOL. 4 DECEMBER1994