High impact information on CLB2

• Yeast Hct1 is a regulator of Clb2 cyclin proteolysis [1].
• Remarkably, Clb2-Cdc28 activity remains elevated in the overreplicating cells [2].
• Proteolysis of CLB2 is initiated in early anaphase, but a fraction of CLB2 remains stable until anaphase is complete [3].
• Neither CLB1 nor CLB2 is essential; however, disruption of both is lethal and causes a mitotic defect [4].
• Fkh2 protein is associated with the promoters of CLB2, SWI5 and other genes of the cluster [5].

Biological context of CLB2

• We show here that CLB2 proteolysis, which is important for transition from mitosis to G1, is not confined to a narrow window at the end of mitosis as previously thought but continues until reactivation of CDC28 by CLN cyclins toward the end of the subsequent G1 period [6].
• This cell cycle arrest can be overcome and partial suppression of the ts phenotype of rts1-null cells occurs if the gene CLB2, encoding a Cdc28 kinase-associated B-type cyclin, is expressed on a high-copy-number plasmid [7].
• However, CLB2 overexpression has no suppressive effects on other aspects of the rts1-null phenotype [7].
• Overproduction of Ndd1 also enhances the expression of SWI5, whose transcription, like that of CLB1 and CLB2, is activated in the late S phase [8].
• BACKGROUND: The 'CLB2 cluster' in Saccharomyces cerevisiae consists of approximately 33 genes whose transcription peaks in late G2/early M phase of the cell cycle [9].

Anatomical context of CLB2

• Our experiments also suggest that NAP1 is required for the ability of the Clb2/p34CDC28 kinase complex to amplify its own production, and that NAP1 plays a role in regulation of microtubule dynamics during mitosis [10].

Associations of CLB2 with chemical compounds

• A malachite green binding motif, defined by an asymmetric internal loop flanked by short RNA helices, was inserted immediately upstream of the CLB2 start codon [11].
• We report here that cells expressing cdc28-E19 (in which Tyr-19 is replaced by glutamic acid) perform Start-related functions, complete DNA synthesis, and exhibit high levels of Clb2-associated kinase activity but are unable to form bipolar spindles [12].
• A point mutation in a potential leucine-rich nuclear export signal (NES) enhances the nuclear localization of the protein, and delta-yrb2 cells exhibit an apparent Clb2p nuclear export defect [13].
• The proline-directed phosphatase, Cdc14p, is a key component of MEN and promotes mitotic exit by activating the degradation of Clb2p and by reversing Cdk-mediated mitotic phosphorylation [14].

Physical interactions of CLB2

• Instead, overexpression of NDD1 prevents the formation of one of the complexes whose appearance correlates with the termination of CLB2 expression in G1 [8].
• The essential transcription factor Reb1p interacts with the CLB2 UAS outside of the G2/M control region [15].
• The forkhead transcription factor Fkh2p acts in a DNA-bound complex with Mcm1p and the coactivator Ndd1p to regulate cell cycle-dependent expression of the CLB2 gene cluster in Saccharomyces cerevisiae [16].
• Active Clb2-Cdc28 kinase complex was purified from yeast cells after inserting the CHH tag into Clb2 [17].

Co-localisations of CLB2

• Clb2 co-localizes with the bud site selection protein Bud3 [18].

Regulatory relationships of CLB2

• We replaced the early-expressed CLB5 coding sequence with the late-expressed CLB2 coding sequence, at the CLB5 locus [19].
• Genetic experiments revealed that loss of either Clb5p or Clb2p cyclins suppresses the mcm5-bob1 mutation and prevents bypass [20].
• In Saccharomyces cerevisiae, Fkh2 both activates and represses transcription of CLB2, encoding a B-type cyclin [21].
• These data show that PKA pathways regulate mitotic progression through Cdc20 and support the DNA damage checkpoint pathways in regulating the destruction of Clb2 and securin [22].
• Furthermore, we find that inactivation of Cln- and Clb-Cdc28 kinases is sufficient to trigger Clb2 proteolysis and sister-chromatid separation in G2/M phase-arrested cells, where the B-type cyclin-specific proteolysis machinery is normally inactive [23].

Other interactions of CLB2

• CLB5 transcript abundance peaks in G1, coincident with the CLN2 transcript but earlier than the CLB2 transcript [24].
• They are most related to each other and then to the deduced protein sequence of their adjacent genes CLB1 and CLB2 [25].
• However, constitutive CLB2 expression does not suppress the mitotic defect, and therefore other essential activities required for the G2-to-M transition must also depend on Mcm1 function [26].
• The Rad50 pathway was more sensitive to the absence of Clb2 than the Rad51 pathway [27].
• We show that both FKH1 and FKH2 play essential roles in the activation of the CLB2 cluster genes during G2-M and in establishing their transcriptional periodicity [9].

Analytical, diagnostic and therapeutic context of CLB2

• Quantification of CLB2 expression at the RNA and protein levels by RT-PCR and Western blot analysis, respectively, demonstrates that the aptamer ligand regulates transcript translatability rather than stability [11].
• Correlating with this phenotype, bud3(Delta1221) cells exhibit a pronounced (15-30 minutes) delay in cytokinesis and/or cell separation, suggesting an unanticipated function of Clb2 in these late mitotic events [18].
• The exit from mitosis is monitored by Cdc14 immunofluorescence and Clb2 Western blots [28].

References