A novel Cdc20-related WD-repeat protein, Fzr1, is required for spore formation in Schizosaccharomyces pombe
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O R I GI N A L P A P E R
H. Asakawa á K. Kitamura á C. Shimoda
A novel Cdc20-related WD-repeat protein, Fzr1, is required for spore formation in Schizosaccharomyces pombe
Received: 4 September 2000 / Accepted: 23 November 2000 / Published online: 20 March 2001 Ó Springer-Verlag 2001
Abstract Ste9/Srw1, which shows sequence homology to Hct1 from budding yeast, is an activator of the anaphase-promoting complex (APC) in the ®ssion yeast Schizosaccharomyces pombe. By homology search of the S. pombe genome, we identi®ed the gene fzr1+, which encodes the protein with the highest homology to Ste9 among ®ve Cdc20-like proteins. Like Ste9, Fzr1 contains seven WD-repeats in its C-terminal region. In spite of this structural similarity, however, overproduction of either of these proteins cannot complement mutants lacking the other. fzr1+ is transcribed exclusively during meiosis and sporulation, suggesting that it plays a role in these processes. In fact, the fzr1 disruptant formed aberrant asci, which contained only one or two mature spores, though meiotic nuclear divisions proceeded with kinetics similar to wild type, and meiotic segregation of chromosomes was normal. Structural alteration of spindle pole bodies, which is a prerequisite for the formation of the forespore membrane, occurred normally in fzr1D during the second meiotic division. Localization of spore rim marker proteins fused to green ¯uorescent protein showed that nascent prespores were irregularly shaped, small in size and few in number in fzr1D cells compared to wild-type cells. Furthermore, electron microscopy revealed that the outer layer of the spore walls was often missing in fzr1D spores. These results show that Fzr1 is speci®cally involved in the assembly of the spore envelope and also in spore maturation. Fzr1, a structural homolog of the APC regulator, therefore plays an important role in spore morphogenesis.
Communicated by: K. Isono H. Asakawa á C. Shimoda (&) Department of Biology, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan E-mail: [email protected] Fax: +81-66605-3158 K. Kitamura Center for Gene Science, Hiroshima University, Kagamiyama, Higashi-Hiroshima 739-8527, Japan
Key words Cdc20/Cdh1 family á Forespore membrane á Meiosis á Sporulation á Ste9
Introduction Mitosis is a fundamental process for all eukaryotes, in which a set of chromosomes are condensed, separated, and distributed to daughter cells. Some steps in mitosis are regulated by ubiquitin-mediated proteolysis of key regulators. Thus, sister chromatid separation requires degradation of a protein called securin ± Cut2 in Schizosaccharomyces pombe and Pds1 in Saccharomyces cerevisiae (Funabiki et al. 1996; Yamamoto et al. 1996; Ciosk et al. 1998). Exit from mitosis requires degradation of mitotic cyclins (Amon et al. 1994; Schwab et al. 1997). Regulated proteolysis of these key molecules is dependent on the anaphase-promoting complex (APC)/ cyclosome, a multi-subunit E3 ubiquitin ligase (for review, see Zachariae and Nasmyth 19
