R Li, C Havel, JA Watson, and AW Murray. 1993. “The mitotic feedback control gene MAD2 encodes the alpha-subunit of a prenyltransferase.” Nature, 366, 6450, Pp. 82-4. Publisher's VersionAbstract
The mad2-1 mutation inactivates the cell-cycle feedback control that prevents budding yeast cells from leaving mitosis until spindle assembly is complete. The gene product of MAD2 shows significant sequence similarity to the alpha-subunit of prenyltransferases. Here we isolate a new temperature-sensitive mad2 mutant, mad2-2ts, and find that Mad2p is required for the membrane association of Ypt1p and Sec4p, two prenylated small GTP-binding proteins involved in protein trafficking. Extracts from mad2-2ts mutant cells fail to geranylgeranylate a number of substrates at the non-permissive temperature. mad2-2ts is synthetically lethal with bet2-1, a mutation in the gene that encodes for the beta-subunit of the Ypt1p and Sec4p geranylgeranyl transferase. Therefore MAD2 and BET2 gene products may physically interact to form a geranylgeranyl transferase complex. In addition, the difference between the phenotypes of mad2-1 and mad2-2ts suggests that MAD2 has distinct roles in protein transport and the mitotic feedback control.
AW Murray. 1992. “Creative blocks: cell-cycle checkpoints and feedback controls.” Nature, 359, 6396, Pp. 599-604. Publisher's VersionAbstract
Before division, cells must ensure that they finish DNA replication, DNA repair and chromosome segregation. They do so by using feedback controls which can detect the failure to complete replication, repair or spindle assembly to arrest the progress of the cell cycle at one of three checkpoints. Failures in feedback controls can contribute to the generation of cancer.
MS Boguski, AW Murray, and S Powers. 1992. “Novel repetitive sequence motifs in the alpha and beta subunits of prenyl-protein transferases and homology of the alpha subunit to the MAD2 gene product of yeast.” New Biol, 4, 4, Pp. 408-11. Publisher's Version
CE Shamu and AW Murray. 1992. “Sister chromatid separation in frog egg extracts requires DNA topoisomerase II activity during anaphase.” J Cell Biol, 117, 5, Pp. 921-34. Publisher's VersionAbstract
We have produced metaphase spindles and induced them to enter anaphase in vitro. Sperm nuclei were added to frog egg extracts, allowed to replicate their DNA, and driven into metaphase by the addition of cytoplasm containing active maturation promoting factor (MPF) and cytostatic factor (CSF), an activity that stabilizes MPF. Addition of calcium induces the inactivation of MPF, sister chromatid separation and anaphase chromosome movement. DNA topoisomerase II inhibitors prevent chromosome segregation at anaphase, demonstrating that the chromatids are catenated at metaphase and that decatenation occurs at the start of anaphase. Topoisomerase II activity towards exogenous substrates does not increase at the metaphase to anaphase transition, showing that chromosome separation at anaphase is not triggered by a bulk activation of topoisomerase II.
PK Sorger and AW Murray. 1992. “S-phase feedback control in budding yeast independent of tyrosine phosphorylation of p34cdc28.” Nature, 355, 6358, Pp. 365-8. Publisher's VersionAbstract
In somatic cells, entry into mitosis depends on the completion of DNA synthesis. This dependency is established by S-phase feedback controls that arrest cell division when damaged or unreplicated DNA is present. In the fission yeast Schizosaccharomyces pombe, mutations that interfere with the phosphorylation of tyrosine 15 (Y15) of p34cdc2, the protein kinase subunit of maturation promoting factor, accelerate the entry into mitosis and abolish the ability of unreplicated DNA to arrest cells in G2. Because the tyrosine phosphorylation of p34cdc2 is conserved in S. pombe, Xenopus, chicken and human cells, the regulation of p34cdc2-Y15 phosphorylation could be a universal mechanism mediating the S-phase feedback control and regulating the initiation of mitosis. We have investigated these phenomena in the budding yeast Saccharomyces cerevisiae. We report here that the CDC28 gene product (the S. cerevisiae homologue of cdc2) is phosphorylated on the equivalent tyrosine (Y19) during S phase but that mutations that prevent tyrosine phosphorylation do not lead to premature mitosis and do not abolish feedback controls. We have therefore demonstrated a mechanism that does not involve tyrosine phosphorylation of p34 by which cells arrest their division in response to the presence of unreplicated or damaged DNA. We speculate that this mechanism may not involve the inactivation of p34 catalytic activity.
AW Murray. 1991. “Cell Biology. Never-in-mitosis in mitosis.” Nature, 353, 6346, Pp. 701-2. Publisher's Version
AW Murray. 1991. “Cell biology. Remembrance of things past.” Nature, 349, 6308, Pp. 367-8. Publisher's Version
AW Murray. 1991. “Cell cycle extracts.” Methods Cell Biol, 36, Pp. 581-605. Publisher's Version
AW Murray. 1991. “Coordinating cell cycle events.” Cold Spring Harb Symp Quant Biol, 56, Pp. 399-408. Publisher's Version
M Glotzer, AW Murray, and MW Kirschner. 1991. “Cyclin is degraded by the ubiquitin pathway.” Nature, 349, 6305, Pp. 132-8. Publisher's VersionAbstract
Cyclin degradation is the key step governing exit from mitosis and progress into the next cell cycle. When a region in the N terminus of cyclin is fused to a foreign protein, it produces a hybrid protein susceptible to proteolysis at mitosis. During the course of degradation, both cyclin and the hybrid form conjugates with ubiquitin. The kinetic properties of the conjugates indicate that cyclin is degraded by ubiquitin-dependent proteolysis. Thus anaphase may be triggered by the recognition of cyclin by the ubiquitin-conjugating system.
R Li and AW Murray. 1991. “Feedback control of mitosis in budding yeast.” Cell, 66, 3, Pp. 519-31. Publisher's VersionAbstract
We have investigated the feedback control that prevents cells with incompletely assembled spindles from leaving mitosis. We isolated budding yeast mutants sensitive to the anti-microtubule drug benomyl. Mitotic arrest-deficient (mad) mutants are the subclass of benomyl-sensitive mutants in which the completion of mitosis is not delayed in the presence of benomyl and that die as a consequence of their premature exit from mitosis. A number of properties of the mad mutants indicate that they are defective in the feedback control over the exit from mitosis: their killing by benomyl requires passage through mitosis; their benomyl sensitivity can be suppressed by an independent method for delaying the exit from mitosis; they have normal microtubules; and they have increased frequencies of chromosome loss. We cloned MAD2, which encodes a putative calcium-binding protein whose disruption is lethal. We discuss the role of feedback controls in coordinating events in the cell cycle.
AW Murray and MW Kirschner. 1991. “What controls the cell cycle?” Sci Am, 264, 3, Pp. 56-63. Publisher's Version
J Minshull, A Murray, A Colman, and T Hunt. 1991. “Xenopus oocyte maturation does not require new cyclin synthesis.” J Cell Biol, 114, 4, Pp. 767-72. Publisher's VersionAbstract
Progesterone induces fully grown, stage VI, Xenopus oocytes to pass through meiosis I and arrest in metaphase of meiosis II. Protein synthesis is required twice in this process: in order to activate maturation promoting factor (MPF) which induces meiosis I, and then again after the completion of meiosis I to reactivate MPF in order to induce meiosis II. We have used antisense oligonucleotides to destroy maternal stores of cyclin mRNAs, and demonstrate that new cyclin synthesis is not required for entry into either meiosis I or II. This finding is consistent with the demonstration that stage VI oocytes contain a store of B-type cyclin polypeptides (Kobayashi, H., J. Minshull, C. Ford, R. Golsteyn, R. Poon, and T. Hunt. 1991. J. Cell Biol. 114:755-765). Although approximately 70% of cyclin B2 is destroyed at first meiosis, the surviving fraction, together with a larger pool of surviving cyclin B1, must be sufficient to allow the reactivation of MPF and induce entry into second meiotic metaphase. Since stage VI oocytes do not contain any cyclin A, our results show that cyclin A is not required for meiosis in Xenopus. We discuss the possible nature of the proteins whose synthesis is required to induce meiosis I and II.
A Murray. 1990. “Telomeres. All's well that ends well.” Nature, 346, 6287, Pp. 797-8. Publisher's Version
AW Murray. 1989. “The cell cycle.” American Zoologist, 29, 2, Pp. 511-522 . Publisher's Version
AW Murray. 1989. “Cell biology: the cell cycle as a cdc2 cycle.” Nature, 342, 6245, Pp. 14-5. Publisher's Version
AW Murray. 1989. “Cyclin synthesis and degradation and the embryonic cell cycle.” J Cell Sci Suppl, 12, Pp. 65-76. Publisher's VersionAbstract
I discuss recent advances in the study of somatic and embryonic cell cycles. In the frog embryonic cell cycle, cyclin is the only newly synthesized protein required to activate maturation-promoting factor and induce mitosis. Diminishing the rate of cyclin synthesis increases the length of interphase. Cyclin degradation is required for the progression from mitosis to interphase. Comparison of the frog embryonic cell cycle to other cell cycles suggests that all cell cycles will rely on the same closely conserved set of components. However, the component that is rate-limiting for any step in the cell cycle will vary in different cell cycles.
AW Murray and MW Kirschner. 1989. “Cyclin synthesis drives the early embryonic cell cycle.” Nature, 339, 6222, Pp. 275-80. Publisher's VersionAbstract
We have produced extracts of frog eggs that can perform multiple cell cycles in vitro. Destruction of the endogenous messenger RNA arrests the extracts in interphase. The addition of exogenous cyclin mRNA is sufficient to produce multiple cell cycles. The newly synthesized cyclin protein accumulates during each interphase and is degraded at the end of each mitosis.
AW Murray and MW Kirschner. 1989. “Dominoes and clocks: the union of two views of the cell cycle.” Science, 246, 4930, Pp. 614-21. Publisher's VersionAbstract
We review the recent advances in understanding transitions within the cell cycle. These have come from both genetic and biochemical approaches. We discuss the phylogenetic conservation of the mechanisms that induce mitosis and their implications for other transitions in the cell cycle.
AW Murray, MJ Solomon, and MW Kirschner. 1989. “The role of cyclin synthesis and degradation in the control of maturation promoting factor activity.” Nature, 339, 6222, Pp. 280-6. Publisher's VersionAbstract
We show that cyclin plays a pivotal role in the control of mitosis. A proteolysis-resistant mutant of cyclin prevents the inactivation of maturation promoting factor and the exit from mitosis both in vivo and in vitro. We have used a fractionated extract to study the activation of MPF by added cyclin protein.