Fission yeast genes involved in coupling mitosis to completion of DNA replication.

Abstract

We have isolated fission yeast mutants that enter mitosis when DNA replication is blocked with hydroxyurea. The mutants define eight linkage groups, three of which consist of alleles of the radl, rad3, and radl 7 genes. Recently, these fission yeast genes have been shown to be required for radiation-induced cell cycle arrest, as is the budding yeast RAD9 gene. The other five genes are called bus (hydroxy_urea sensitive) 1-5. We propose that these genes participate in an intraceUular signal transduction pathway that monitors the completion of DNA replication and transmits information to the mitotic control protein cdc2. Mutations that bypass the requirement for cdc25 (an activator of the mitotic regulator cdc2) also uncouple mitosis from DNA replication. However, mitosis is blocked by inhibitors of DNA replication in strains in which the cdc25 gene has been deleted, indicating that although cdc25 influences the coupling of mitosis to the completion of DNA replication, it is not essential for this control.[Key Words: Cell cycle; checkpoint; radiation; cdc25; S. pombe] Received May 4, 1992; revised version accepted August 27, 1992.A normal cell cycle consists of a temporally ordered series of events. This order is maintained partly by mechanisms that can monitor completion of earlier events, called "checkpoint" (Hartwell and Weinert 1989) or "feedback" (Murray and Kirschner 1989)controls. Elimination of such controls by mutation or chemical treatment disrupts the dependencies characteristic of ordered progression through the cell cycle (for review, see Hartwell and Weinert 1989). Although mutations that abolish several different cell cycle checkpoints have been identified (Weinert and Hartwell 1988;Hoyt et al. 1991;Li and Murray 1991), it is not clear how these controls work. Early steps must "signal" late steps, but little is known about what these signals are or how they are monitored.We are investigating this problem by studying the coupling of mitosis to the completion of DNA replication in the fission yeast Schizosaccharomyces pombe. This sys-

Mis3 with a conserved RNA binding motif is essential for ribosome biogenesis and implicated in the start of cell growth and S phase checkpoint

“…The double mutants between mis3-224 (Takahashi et al e1994) and various mutations noted below were constructed; cdc2-33, cdc6-121, cdc13-117, cdc25-22, cdc10-129 (Nurse et al 1976), cdc2-3w (Enoch et al 1992), Dcyc17/cig2 (Obara-Ishihara & Okayama 1994), Dmik1 (Lundgren et al 1991), wee1-50 (Russell & Nurse 1987), cdc16-116 (Fankhauser et al 1993), cdc17-K42, cdc18-K46 (Nasmyth & Nurse 1981), cdc22-C1 (Fernandez Sarabia et al 1993), swi7-H4 (Singh & Klar 1993), mis5-268, mis11-453 (Takahashi et al 1994, Drad3, Drad9, Drad17, Drad24, Drad25, Dchk1 (Al-Khodairy et al 1994), cut5-T401 (Saka et al 1994), Dcds1 (Murakami & Okayama 1995), Ddis1 (Nabeshima et al 1995), dis3-54 (Kinoshita et al 1991), dis2-11, Ddis2 (Ohkura et al 1989), cut1-21, cut2-364 (Funabiki et al 1996, cut9 (Yamada et al 1997), Dppa1, Dppa2 (Kinoshita et al 1993),Dpck1 (Toda et al 1993), Dtop1, top2-191 (Uemura & Yanagida 1984), and Ddsk1 mutants (Takeuchi & Yanagida 1993). The Mis3-HA integrant was obtained by integrating the HA-tagged mis3 gene at the carboxyl-terminus to replace the genomic mis3 locus.…”

“…Cdc2 kinase plays a key role in ordering the S and M phase (Nurse 1994;MacNeill & Nurse 1997), but little is known of how cells control the onset and duration for the periods of cell mass increase in interphase cell cycle stages. If coordinating control between cell mass and cell cycle is abolished, cells may enter a lethal stage with activation of CDK (cyclin dependent kinase) before reaching normal cell size (Lundgren et al 1991;Enoch et al 1992). It is known that tyrosine phosphorylation at Y15 controls the Cdc2 kinase activity and is important for cell cycle control (Russell & Nurse 1986.…”

Mitotic DNA damage and replication checkpoints in yeast

“…The checkpoint rad genes include rad1 sp , rad3 sp , rad9 sp , rad17 sp , rad26 sp , and hus1 sp . These are required for all the known S. pombe DNA checkpoints [3,13,14]. At the very least, the checkpoint rad gene products serve as signal transducers between the primary checkpoint signal and the cell cycle machinery.…”

“…In addition to having the same ultimate target, the S/M checkpoint shares the upstream checkpoint Rad proteins with the G 2 DNA damage checkpoint [13,14]. It is possible that all the checkpoint rad genes are required for both G 2 /M checkpoints because they sense the same primary signal in both cases, perhaps single stranded DNA.…”

“…Cds1 sp has roles in HU resistance that are independent of its checkpoint function. In the absence of Cds1 sp , or any of the checkpoint Rad proteins, cells rapidly lose viability, independent of the failure to prevent mitosis [13,75]. It is thought that this loss of viability reflects a role for Cds1 sp , termed its recovery function, in stabilizing stalled replication forks.…”