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Gene Review

CLB1  -  Clb1p

Saccharomyces cerevisiae S288c

Synonyms: G2/mitotic-specific cyclin-1, G5967, SCB1, YGR108W
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High impact information on CLB1

  • Neither CLB1 nor CLB2 is essential; however, disruption of both is lethal and causes a mitotic defect [1].
  • Three of these (CLB1, CLB2, and CLB4) encode proteins strongly homologous to G2-specific B-type cyclins [1].
  • Levels of SCB1 mRNA and protein were found to be periodic through the cell cycle, with maximum accumulation late, most likely in the G2 interval [2].
  • A mutant allele of SCB1 that removes an amino-terminal fragment of the encoded protein thought to be required for efficient degradation during mitosis confers a mitotic arrest phenotype [2].
  • Using clb1,2,3,4 cells rescued by conditional overproduction of CLB1, we showed that the CLB genes perform an essential role at the G2/M-phase transition, and also a role in S phase [3].

Biological context of CLB1


Regulatory relationships of CLB1

  • Third, ectopic overexpression of AMA1 is able to stimulate ubiquitination of Clb1p in vitro and degradation of Clb1p in vivo [9].

Other interactions of CLB1

  • The previously described CLB1 and CLB2 genes encode a closely related pair of B-type cyclins [10].
  • Ndd1 is essential for the expression of CLB1, CLB2, and SWI5, since none of these genes are transcribed in its absence [6].
  • The recent finding that individual B-type cyclins (encoded by the genes CLB1-CLB6) can have functions in both processes in the budding yeast Saccharomyces cerevisiae casts doubt on this notion [11].
  • In contrast, SBF dissociates from the CLN2 promoter when transcription is repressed during G2 and M phases, suggesting that Clb1-Clb4 repress SBF activity by inhibiting its DNA-binding activity [12].
  • Second, Ama1p is required for the degradation of the B-type cyclin Clb1p, an APC/C substrate in both meiotic and mitotic cells [9].

Analytical, diagnostic and therapeutic context of CLB1


  1. The role of CDC28 and cyclins during mitosis in the budding yeast S. cerevisiae. Surana, U., Robitsch, H., Price, C., Schuster, T., Fitch, I., Futcher, A.B., Nasmyth, K. Cell (1991) [Pubmed]
  2. A cyclin B homolog in S. cerevisiae: chronic activation of the Cdc28 protein kinase by cyclin prevents exit from mitosis. Ghiara, J.B., Richardson, H.E., Sugimoto, K., Henze, M., Lew, D.J., Wittenberg, C., Reed, S.I. Cell (1991) [Pubmed]
  3. Cyclin-B homologs in Saccharomyces cerevisiae function in S phase and in G2. Richardson, H., Lew, D.J., Henze, M., Sugimoto, K., Reed, S.I. Genes Dev. (1992) [Pubmed]
  4. Specialization of B-type cyclins for mitosis or meiosis in S. cerevisiae. Dahmann, C., Futcher, B. Genetics (1995) [Pubmed]
  5. Mcm1 is required to coordinate G2-specific transcription in Saccharomyces cerevisiae. Althoefer, H., Schleiffer, A., Wassmann, K., Nordheim, A., Ammerer, G. Mol. Cell. Biol. (1995) [Pubmed]
  6. NDD1, a high-dosage suppressor of cdc28-1N, is essential for expression of a subset of late-S-phase-specific genes in Saccharomyces cerevisiae. Loy, C.J., Lydall, D., Surana, U. Mol. Cell. Biol. (1999) [Pubmed]
  7. The pachytene checkpoint in S. cerevisiae depends on Swe1-mediated phosphorylation of the cyclin-dependent kinase Cdc28. Leu, J.Y., Roeder, G.S. Mol. Cell (1999) [Pubmed]
  8. Cdc28 and Ime2 possess redundant functions in promoting entry into premeiotic DNA replication in Saccharomyces cerevisiae. Guttmann-Raviv, N., Boger-Nadjar, E., Edri, I., Kassir, Y. Genetics (2001) [Pubmed]
  9. Ama1p is a meiosis-specific regulator of the anaphase promoting complex/cyclosome in yeast. Cooper, K.F., Mallory, M.J., Egeland, D.B., Jarnik, M., Strich, R. Proc. Natl. Acad. Sci. U.S.A. (2000) [Pubmed]
  10. Characterization of four B-type cyclin genes of the budding yeast Saccharomyces cerevisiae. Fitch, I., Dahmann, C., Surana, U., Amon, A., Nasmyth, K., Goetsch, L., Byers, B., Futcher, B. Mol. Biol. Cell (1992) [Pubmed]
  11. S-phase-promoting cyclin-dependent kinases prevent re-replication by inhibiting the transition of replication origins to a pre-replicative state. Dahmann, C., Diffley, J.F., Nasmyth, K.A. Curr. Biol. (1995) [Pubmed]
  12. Switching transcription on and off during the yeast cell cycle: Cln/Cdc28 kinases activate bound transcription factor SBF (Swi4/Swi6) at start, whereas Clb/Cdc28 kinases displace it from the promoter in G2. Koch, C., Schleiffer, A., Ammerer, G., Nasmyth, K. Genes Dev. (1996) [Pubmed]
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