The S. pombe cdc16 gene is required both for maintenance of p34cdc2 kinase activity and regulation of septum formation: a link between mitosis and cytokinesis?

Abstract

In the fission yeast Schizosaccharomyces pombe, septum formation and cytokinesis are dependent upon the initiation, though not the completion of mitosis. A number of cell cycle mutants which show phenotypes consistent with a defect in the regulation of septum formation have been isolated. A mutation in the S.pombe cdc16 gene leads to the formation of multiple septa without cytokinesis, suggesting that the normal mechanisms that limit the cell to the formation of a single septum in each cycle do not operate. Mutations in the S.pombe early septation mutants cdc7, cdcll, cdc14 and cdc15 lead to the formation of elongated, multinucleate cells, as a result of S phase and mitosis continuing in the absence of cytokinesis. This suggests that in these cells, the normal mechanisms which initiate cytokinesis are defective and that they are unable to respond to this by preventing further nuclear cycles. Genetic analysis has implied that the products of some of these genes may interact with that of the cdc16 gene. To understand how the processes of septation and cytokinesis are regulated and coordinated with mitosis we are studying the early septation mutants and cdc16. In this paper, we present the cloning and analysis of the cdc16 gene. Deletion of the gene shows that it is essential for cell proliferation: spores lacking a functional cdc16 gene germinate, complete mitosis and form multiple septa without undergoing cell cleavage. Examination of the activity of p34Cdc2 kinase in the cdcl6-116 mutant shows that, after shift to the non-permissive temperature, mitotic p34M2 kinase activity decays rapidly and cells fail to respond normally to the absence of the mitotic spindle, initiating septum formation even if mitosis has not been completed. The sequence of the predicted gene product shows homology to the BUB2 gene of Saccharomyces cerevisiae. Expression of the BUB2 gene in S.pombe will rescue the cdcl6-116 mutant, but not a null allele. The cdc16 gene product may be part of a feedback mechanism preventing premature exist from mitosis by maintaining high levels of p34'd2 activity until the initiation of anaphase, thereby coordinating mitosis with septation, cytokinesis and entry into the next cycle.

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.…”

Localization of Fission Yeast Type II Myosin, Myo2, to the Cytokinetic Actin Ring Is Regulated by Phosphorylation of a C-Terminal Coiled-Coil Domain and Requires a Functional Septation Initiation Network

“…All of these components, with the exception of Sid1, have homologs in the budding yeast mitotic exit network (Hoyt, 2000). Mutations in Cdc7, Sid1, Sid2, and Spg1 abolish septation, whereas mutations in Cdc16 and Byr4 drive cells into cytokinesis and they become multiseptate (Minet et al, 1979;Fankhauser et al, 1993). A similar phenotype is seen when Cdc7 and Spg1 are overexproduced (Fankhauser and Simanis, 1994;Schmidt et al, 1997).…”

A novel suppressor of ras1 in fission yeast, byr4, is a dosage-dependent inhibitor of cytokinesis.

“…Tetrads from CA103 were dissected to determine the effect of deletion of byr4. For germination of spores in liquid culture, CA103 was grown to midexponential phase in YE and then transferred to MM sporulation media (MM-glu with 1% glucose) (Fankhauser et al, 1993;Hagan and Hyams, 1988). After growth for 48 h in MM sporulation media, vegetative cells were lysed by treatment with 0.5% (vol/vol) glusulase (DuPont, Wilmington, DE) for 24 h at 29°C.…”