BCK2

Last updated
BCK2
Identifiers
Organism Saccharomyces cerevisiae S288C
SymbolBCK2
Alt. symbolsCTR7
Entrez 856914
RefSeq (mRNA) NM_001179057.3
RefSeq (Prot) NP_011094.3
UniProt P33306
Other data
Chromosome V: 0.52 - 0.52 Mb
Search for
Structures Swiss-model
Domains InterPro

BCK2, also named CTR7, is an early cell cycle regulator expressed by the yeast Saccharomyces cerevisiae . It was first discovered in a screen for genes whose overexpression would suppress the phenotypes of PKC1 pathway mutations (thus named Bypass of CKinase). [1] Though its mechanism is currently unknown, it is believed to interact with Swi4 and Mcm1, both important transcriptional regulators of early cell cycle.

Contents

Discovery

BCK2 was first discovered in a yeast genomic library screen. An mpk1 deletion strain was transformed with a library of plasmid vectors containing parts of the entire yeast genome. One of the cells that grew out harbored BCK2 on its plasmid, whose overexpression rescued the mpk1 deletion phenotype. In the same publication, Bck2 was found to rescue a pck1 deletion phenotype as well.[ citation needed ]

Protein structure

BCK2 encodes a 93.7 kDa protein that is 851 amino acids long. [2] The protein is serine/threonine-rich. [1] The expression of BCK2 with a deletion of 189 amino acids of the C-terminus resulted in the loss of CLN3 and BCK2 deletion phenotype. A crystal structure of Bck2 has not been determined.[ citation needed ]

Genetics

BCK2 loss results in larger cell size resulting from delay of START, a checkpoint in the yeast cell cycle. [3] [4] A double deletion of BCK2 and G1 cyclin CLN3 results in inviability [3] or extremely slow growth. [4] This was found to be a result of G1 arrest [5] Overexpression of CLN2 or RME1 (a transcriptional activator of CLN2) was found to rescue loss of BCK2 and CLN3. [5] Loss of BCK2 also led to a decrease in rate and levels of CLN2 mRNA accumulation in G1, as well as a delay in SWI4 mRNA accumulation. [4]

Overexpression of BCK2 resulted in smaller cell size. [4] Besides rescuing PCK1 pathway mutation phenotypes1, overexpression of BCK2 also rescued the slow growth rate phenotype of a CLN2- and CLN3-null strain. [4]

Physical interactions

A yeast two-hybrid screen revealed that Bck2 physically interacts with Mcm1, Swi4, Yap6, and Mot3. [6] A V69E mutation on a hydrophobic pocket in Mcm1 prevents binding of Yox1 and Fkh2. [7] This same mutation resulted in loss of interaction with Bck2. [6]

Cell cycle regulation

The overexpression and null genetic experiments performed with BCK2 suggests its role as a G1 cell cycle regulator. For example, BCK2-null is synthetically lethal with G1 cyclin CLN3, [3] [4] and leads to a decrease in mRNA levels of another G1 cyclin CLN2 and transcriptional regulator of late-G1 genes SWI4 [4] .

A global screen for genes regulated by Bck2 investigated through RNA microarray experiments revealed that Bck2 regulated a wide range of cell cycle genes beyond those associated with G1 phase. [8] The SBF and MBF complexes, which includes protein Swi6, regulate late G1 and G1/S transition genes. Overexpression of Bck2 in Swi6-null cells resulted in changes in expression of genes known to be regulators of the cell cycle, or cell cycle dependent. [8]

40% of the genes found to be regulated by Bck2 were also targets of regulation by Mcm1. Mcm1 activates M/G1 genes through binding to promoters containing Early Cell Cycle Box (ECB) elements. [9] Another study showed gene regulation by Bck2 may be ECB-dependent. BCK2 overexpression leads to CLN3 and SWI4 upregulation. Mutations of ECB elements in CLN3 and SWI4 promoters blocked these effects. [6]

Bck2 may also be sensing cell size to promote crossing of START. Budding yeast senses cell size at START in part through sensing Whi5 concentrations in G1. Cells express the same amount of Whi5 protein independent of size, leading to larger cells having lower concentrations of Whi5. [10] Thus, larger cells take a shorter amount of time from birth to START. Expressing multiple copies of WHI5 led to a linear increase in this time. Importantly, this effect was observed to be greater in BCK2 deletion backgrounds, [10] suggesting that BCK2 may also be sensing cell size to input signals for passing START.

Related Research Articles

<span class="mw-page-title-main">Cell cycle</span> Series of events and stages that result in cell division

The cell cycle, or cell-division cycle, is the series of events that take place in a cell that causes it to divide into two daughter cells. These events include the duplication of its DNA and some of its organelles, and subsequently the partitioning of its cytoplasm, chromosomes and other components into two daughter cells in a process called cell division.

G<sub>0</sub> phase Quiescent stage of the cell cycle in which the cell does not divide

The G0 phase describes a cellular state outside of the replicative cell cycle. Classically, cells were thought to enter G0 primarily due to environmental factors, like nutrient deprivation, that limited the resources necessary for proliferation. Thus it was thought of as a resting phase. G0 is now known to take different forms and occur for multiple reasons. For example, most adult neuronal cells, among the most metabolically active cells in the body, are fully differentiated and reside in a terminal G0 phase. Neurons reside in this state, not because of stochastic or limited nutrient supply, but as a part of their developmental program.

<span class="mw-page-title-main">S phase</span> DNA replication phase of the cell cycle, between G1 and G2 phase

S phase (Synthesis Phase) is the phase of the cell cycle in which DNA is replicated, occurring between G1 phase and G2 phase. Since accurate duplication of the genome is critical to successful cell division, the processes that occur during S-phase are tightly regulated and widely conserved.

<span class="mw-page-title-main">Cyclin E</span> Member of the cyclin family

Cyclin E is a member of the cyclin family.

<span class="mw-page-title-main">SCF complex</span>

Skp, Cullin, F-box containing complex is a multi-protein E3 ubiquitin ligase complex that catalyzes the ubiquitination of proteins destined for 26S proteasomal degradation. Along with the anaphase-promoting complex, SCF has important roles in the ubiquitination of proteins involved in the cell cycle. The SCF complex also marks various other cellular proteins for destruction.

<span class="mw-page-title-main">Cyclin D</span> Member of the cyclin protein family

Cyclin D is a member of the cyclin protein family that is involved in regulating cell cycle progression. The synthesis of cyclin D is initiated during G1 and drives the G1/S phase transition. Cyclin D protein is anywhere from 155 to 477 amino acids in length.

<span class="mw-page-title-main">Cyclin-dependent kinase 1</span> Mammalian protein found in Homo sapiens

Cyclin-dependent kinase 1 also known as CDK1 or cell division cycle protein 2 homolog is a highly conserved protein that functions as a serine/threonine protein kinase, and is a key player in cell cycle regulation. It has been highly studied in the budding yeast S. cerevisiae, and the fission yeast S. pombe, where it is encoded by genes cdc28 and cdc2, respectively. With its cyclin partners, Cdk1 forms complexes that phosphorylate a variety of target substrates ; phosphorylation of these proteins leads to cell cycle progression.

<span class="mw-page-title-main">Cyclin E1</span> Protein-coding gene in the species Homo sapiens

G1/S-specific cyclin-E1 is a protein that in humans is encoded by the CCNE1 gene.

G1/S-specific cyclin Cln3 is a protein that is encoded by the CLN3 gene. The Cln3 protein is a budding yeast G1 cyclin that controls the timing of Start, the point of commitment to a mitotic cell cycle. It is an upstream regulator of the other G1 cyclins, and it is thought to be the key regulator linking cell growth to cell cycle progression. It is a 65 kD, unstable protein; like other cyclins, it functions by binding and activating cyclin-dependent kinase (CDK).

<span class="mw-page-title-main">Meiotic recombination checkpoint</span>

The meiotic recombination checkpoint monitors meiotic recombination during meiosis, and blocks the entry into metaphase I if recombination is not efficiently processed.

Epistasis refers to genetic interactions in which the mutation of one gene masks the phenotypic effects of a mutation at another locus. Systematic analysis of these epistatic interactions can provide insight into the structure and function of genetic pathways. Examining the phenotypes resulting from pairs of mutations helps in understanding how the function of these genes intersects. Genetic interactions are generally classified as either Positive/Alleviating or Negative/Aggravating. Fitness epistasis is positive when a loss of function mutation of two given genes results in exceeding the fitness predicted from individual effects of deleterious mutations, and it is negative when it decreases fitness. Ryszard Korona and Lukas Jasnos showed that the epistatic effect is usually positive in Saccharomyces cerevisiae. Usually, even in case of positive interactions double mutant has smaller fitness than single mutants. The positive interactions occur often when both genes lie within the same pathway Conversely, negative interactions are characterized by an even stronger defect than would be expected in the case of two single mutations, and in the most extreme cases the double mutation is lethal. This aggravated phenotype arises when genes in compensatory pathways are both knocked out.

The Start checkpoint is a major cell cycle checkpoint in yeast. The Start checkpoint ensures irreversible cell-cycle entry even if conditions later become unfavorable. The physiological factors that control passage through the Start checkpoint include external nutrient concentrations, presence of mating factor/ pheromone, forms of stress, and size control.

<span class="mw-page-title-main">Cell division control protein 4</span>

Cdc4 is a substrate recognition component of the SCF ubiquitin ligase complex, which acts as a mediator of ubiquitin transfer to target proteins, leading to their subsequent degradation via the ubiquitin-proteasome pathway. Cdc4 targets primarily cell cycle regulators for proteolysis. It serves the function of an adaptor that brings target molecules to the core SCF complex. Cdc4 was originally identified in the model organism Saccharomyces cerevisiae. CDC4 gene function is required at G1/S and G2/M transitions during mitosis and at various stages during meiosis.

Cdc14 and Cdc14 are a gene and its protein product respectively. Cdc14 is found in most of the eukaryotes. Cdc14 was defined by Hartwell in his famous screen for loci that control the cell cycle of Saccharomyces cerevisiae. Cdc14 was later shown to encode a protein phosphatase. Cdc14 is dual-specificity, which means it has serine/threonine and tyrosine-directed activity. A preference for serines next to proline is reported. Many early studies, especially in the budding yeast Saccharomyces cerevisiae, demonstrated that the protein plays a key role in regulating late mitotic processes. However, more recent work in a range of systems suggests that its cellular function is more complex.

<span class="mw-page-title-main">Control of chromosome duplication</span>

In cell biology, eukaryotes possess a regulatory system that ensures that DNA replication occurs only once per cell cycle.

<span class="mw-page-title-main">DNA re-replication</span> Undesirable occurrence in eukaryotic cells

DNA re-replication is an undesirable and possibly fatal occurrence in eukaryotic cells in which the genome is replicated more than once per cell cycle. Rereplication is believed to lead to genomic instability and has been implicated in the pathologies of a variety of human cancers. To prevent rereplication, eukaryotic cells have evolved multiple, overlapping mechanisms to inhibit chromosomal DNA from being partially or fully rereplicated in a given cell cycle. These control mechanisms rely on cyclin-dependent kinase (CDK) activity. DNA replication control mechanisms cooperate to prevent the relicensing of replication origins and to activate cell cycle and DNA damage checkpoints. DNA rereplication must be strictly regulated to ensure that genomic information is faithfully transmitted through successive generations.

The Gal4 transcription factor is a positive regulator of gene expression of galactose-induced genes. This protein represents a large fungal family of transcription factors, Gal4 family, which includes over 50 members in the yeast Saccharomyces cerevisiae e.g. Oaf1, Pip2, Pdr1, Pdr3, Leu3.

<span class="mw-page-title-main">Pdr1p</span>

Pdr1p is a transcription factor found in yeast and is a key regulator of genes involved in general drug response. It induces the expression of ATP-binding cassette transporter, which can export toxic substances out of the cell, allowing cells to survive under general toxic chemicals. It binds to DNA sequences that contain certain motifs called pleiotropic drug response element (PDRE). Pdr1p is encoded by a gene called PDR1 on chromosome VII.

Whi5 is a transcriptional regulator in the budding yeast cell cycle, notably in the G1 phase. It is an inhibitor of SBF, which is involved in the transcription of G1-specific genes. Cln3 promotes the disassociation of Whi5 from SBF, and its disassociation results in the transcription of genes needed to enter S phase.

Induced cell cycle arrest is the use of a chemical or genetic manipulation to artificially halt progression through the cell cycle. Cellular processes like genome duplication and cell division stop. It can be temporary or permanent. It is an artificial activation of naturally occurring cell cycle checkpoints, induced by exogenous stimuli controlled by an experimenter.

References

  1. 1 2 Lee KS, Hines LK, Levin DE (September 1993). "A pair of functionally redundant yeast genes (PPZ1 and PPZ2) encoding type 1-related protein phosphatases function within the PKC1-mediated pathway". Molecular and Cellular Biology. 13 (9): 5843–53. doi:10.1128/mcb.13.9.5843. PMC   360330 . PMID   8395014.
  2. ↑ "BCK2 | SGD". www.yeastgenome.org. Retrieved 2019-12-15.
  3. 1 2 3 Epstein CB, Cross FR (March 1994). "Genes that can bypass the CLN requirement for Saccharomyces cerevisiae cell cycle START". Molecular and Cellular Biology. 14 (3): 2041–7. doi:10.1128/mcb.14.3.2041. PMC   358564 . PMID   8114735.
  4. 1 2 3 4 5 6 7 Di Como CJ, Chang H, Arndt KT (April 1995). "Activation of CLN1 and CLN2 G1 cyclin gene expression by BCK2". Molecular and Cellular Biology. 15 (4): 1835–46. doi:10.1128/mcb.15.4.1835. PMC   230409 . PMID   7891677.
  5. 1 2 Wijnen H, Futcher B (November 1999). "Genetic analysis of the shared role of CLN3 and BCK2 at the G(1)-S transition in Saccharomyces cerevisiae". Genetics. 153 (3): 1131–43. doi:10.1093/genetics/153.3.1131. PMC   1460821 . PMID   10545447.
  6. 1 2 3 Bastajian N, Friesen H, Andrews BJ (May 2013). "Bck2 acts through the MADS box protein Mcm1 to activate cell-cycle-regulated genes in budding yeast". PLOS Genetics. 9 (5): e1003507. doi: 10.1371/journal.pgen.1003507 . PMC   3649975 . PMID   23675312.
  7. ↑ Boros J, Lim FL, Darieva Z, Pic-Taylor A, Harman R, Morgan BA, Sharrocks AD (May 2003). "Molecular determinants of the cell-cycle regulated Mcm1p-Fkh2p transcription factor complex". Nucleic Acids Research. 31 (9): 2279–88. doi:10.1093/nar/gkg347. PMC   154233 . PMID   12711672.
  8. 1 2 Ferrezuelo F, Aldea M, Futcher B (January 2009). "Bck2 is a phase-independent activator of cell cycle-regulated genes in yeast". Cell Cycle. 8 (2): 239–52. doi: 10.4161/cc.8.2.7543 . PMID   19158491.
  9. ↑ McInerny CJ, Partridge JF, Mikesell GE, Creemer DP, Breeden LL (May 1997). "A novel Mcm1-dependent element in the SWI4, CLN3, CDC6, and CDC47 promoters activates M/G1-specific transcription". Genes & Development. 11 (10): 1277–88. doi: 10.1101/gad.11.10.1277 . PMID   9171372.
  10. 1 2 Schmoller KM, Turner JJ, Kõivomägi M, Skotheim JM (October 2015). "Dilution of the cell cycle inhibitor Whi5 controls budding-yeast cell size". Nature. 526 (7572): 268–72. Bibcode:2015Natur.526..268S. doi:10.1038/nature14908. PMC   4600446 . PMID   26390151.
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