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Gene Review

CLB5  -  Clb5p

Saccharomyces cerevisiae S288c

Synonyms: P9642.8, S-phase entry cyclin-5, YPR120C
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High impact information on CLB5


Biological context of CLB5

  • Our observation that CLB5 is involved in the initiation of both S phase and mitosis suggests that a single primordial B-type cyclin might have been sufficient for regulating the cell cycle of the common ancestor of many, if not all, eukaryotes [5].
  • CLB5 and CLB6 are required for premeiotic DNA replication and activation of the meiotic S/M checkpoint [6].
  • By this approach, a novel phenotype associated with CLB5 mutation was observed [7].
  • Thus, CLB5 effects proper preanaphase spindle positioning, yet the requirement differs in haploids and diploids [7].
  • Although cells that lack clb5 and clb6 are unable to activate the meiotic DNA replication checkpoint, they do possess an intact DNA damage checkpoint which can restrain chromosome segregation in the face of DNA damage [6].

Associations of CLB5 with chemical compounds


Physical interactions of CLB5

  • The complementary C-terminal segment of SIC1 binds to the S-phase cyclin CLB5, indicating a modular structure for SIC1 [13].
  • Interaction of the S-phase cyclin Clb5 with an "RXL" docking sequence in the initiator protein Orc6 provides an origin-localized replication control switch [14].

Regulatory relationships of CLB5

  • We replaced the early-expressed CLB5 coding sequence with the late-expressed CLB2 coding sequence, at the CLB5 locus [15].
  • Interestingly, overexpression of Clb5 could induce DNA replication in met30 mutants, albeit very inefficiently [16].
  • Clb6 lacks the destruction box motif responsible for the anaphase promoting complex-mediated destruction of Clb5 but contains putative Cdc4 degron motifs in the N terminus [17].

Other interactions of CLB5

  • Deletion of CLB6 has little or no effect, but deletion of CLB5 greatly extends S phase, and deleting both genes prevents the timely initiation of DNA replication [5].
  • Consistent with this assumption, overproduction of Clb5 greatly enhances the transcription of at least two G(1) cyclin genes (CLN1 and CLN2) in heat-shocked G(1) cells [18].
  • Here we report our finding that the G(1) cyclin Cln3 and the S cyclin Clb5 are the key factors required for recovery from heat shock-induced G(1) arrest [18].
  • In summary, we report numerous genetic interactions and phenotypic descriptions supporting a close functional relationship between the Clb5 cyclin, the PKC pathway, and the Swi4 transcription factor [8].
  • The B-type cyclins Clb5 and Clb6 are the primary activators of the S phase function of the budding yeast CDK Cdc28 [6].


  1. APC-dependent proteolysis of the mitotic cyclin Clb2 is essential for mitotic exit. Wäsch, R., Cross, F.R. Nature (2002) [Pubmed]
  2. APC(Cdc20) promotes exit from mitosis by destroying the anaphase inhibitor Pds1 and cyclin Clb5. Shirayama, M., Tóth, A., Gálová, M., Nasmyth, K. Nature (1999) [Pubmed]
  3. Role of a ubiquitin-conjugating enzyme in degradation of S- and M-phase cyclins. Seufert, W., Futcher, B., Jentsch, S. Nature (1995) [Pubmed]
  4. Regulation of meiotic S phase by Ime2 and a Clb5,6-associated kinase in Saccharomyces cerevisiae. Dirick, L., Goetsch, L., Ammerer, G., Byers, B. Science (1998) [Pubmed]
  5. CLB5 and CLB6, a new pair of B cyclins involved in DNA replication in Saccharomyces cerevisiae. Schwob, E., Nasmyth, K. Genes Dev. (1993) [Pubmed]
  6. CLB5 and CLB6 are required for premeiotic DNA replication and activation of the meiotic S/M checkpoint. Stuart, D., Wittenberg, C. Genes Dev. (1998) [Pubmed]
  7. Clb5-associated kinase activity is required early in the spindle pathway for correct preanaphase nuclear positioning in Saccharomyces cerevisiae. Segal, M., Clarke, D.J., Reed, S.I. J. Cell Biol. (1998) [Pubmed]
  8. Functional connection between the Clb5 cyclin, the protein kinase C pathway and the Swi4 transcription factor in Saccharomyces cerevisiae. Queralt, E., Igual, J.C. Genetics (2005) [Pubmed]
  9. The Cyclin-dependent Kinase Cdc28p Regulates Multiple Aspects of Kar9p Function in Yeast. Moore, J.K., Miller, R.K. Mol. Biol. Cell (2007) [Pubmed]
  10. S-phase cyclins are required for a stable arrest at metaphase. Meyn, M.A., Holloway, S.L. Curr. Biol. (2000) [Pubmed]
  11. DNA damage inhibits proteolysis of the B-type cyclin Clb5 in S. cerevisiae. Germain, D., Hendley, J., Futcher, B. J. Cell. Sci. (1997) [Pubmed]
  12. The regulation of Clb5 kinase activity by mating factor. Jeoung, D.I., Cross, F. Mol. Cells (2000) [Pubmed]
  13. SIC1 is ubiquitinated in vitro by a pathway that requires CDC4, CDC34, and cyclin/CDK activities. Verma, R., Feldman, R.M., Deshaies, R.J. Mol. Biol. Cell (1997) [Pubmed]
  14. Interaction of the S-phase cyclin Clb5 with an "RXL" docking sequence in the initiator protein Orc6 provides an origin-localized replication control switch. Wilmes, G.M., Archambault, V., Austin, R.J., Jacobson, M.D., Bell, S.P., Cross, F.R. Genes Dev. (2004) [Pubmed]
  15. Specialization and targeting of B-type cyclins. Cross, F.R., Yuste-Rojas, M., Gray, S., Jacobson, M.D. Mol. Cell (1999) [Pubmed]
  16. The F-box protein Met30 is required for multiple steps in the budding yeast cell cycle. Su, N.Y., Flick, K., Kaiser, P. Mol. Cell. Biol. (2005) [Pubmed]
  17. Distinct mechanisms control the stability of the related S-phase cyclins Clb5 and Clb6. Jackson, L.P., Reed, S.I., Haase, S.B. Mol. Cell. Biol. (2006) [Pubmed]
  18. Recovery of the yeast cell cycle from heat shock-induced G(1) arrest involves a positive regulation of G(1) cyclin expression by the S phase cyclin Clb5. Li, X., Cai, M. J. Biol. Chem. (1999) [Pubmed]
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