title: Gef1p and Scd1p, the Two GDP-GTP exchange factors for Cdc42p, form a ring structure that shrinks during cytokinesis in Schizosaccharomyces pombe.
abstract: Fission yeast Cdc42p, a small GTPase of the Rho family, is essential for cell proliferation and maintenance of the rod-like cell morphology. Scd1/Ral1p is a GDP-GTP exchange factor (GEF) for Cdc42p. This study and a parallel study by others establish that Gef1p is another GEF for Cdc42p. Deletions of gef1 and scd1 are synthetically lethal, generating round dead cells, and hence mimic the phenotype of cdc42 deletion. Gef1p is localized mainly to the cell division site. Scd1p is also there, but it is also detectable in other parts of the cell, including the nucleus, growing ends, and the tips of conjugation tubes. Gef1p and Scd1p form a ring structure at the cell division site, which shrinks during cytokinesis following the contraction of the actomyosin ring. Formation of the Gef1p/Scd1p ring apparently depends on the integrity of the actomyosin ring. In turn, recruitment of Cdc42p to the cell division site follows the shrinking Gef1p/Scd1p ring; the Cdc42p accumulates like a closing iris. These observations suggest that Gef1p and Scd1p may have a role in mediating between contraction of the actomyosin ring and formation of the septum, by recruiting active Cdc42p to the septation site.
authors.affiliation: Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Hongo, Tokyo 113-0033, Japan.
authors.forename: Kouji
authors.initials: K
authors.lastname: Hirota
authors.forename: Kayoko
authors.initials: K
authors.lastname: Tanaka
authors.forename: Kunihiro
authors.initials: K
authors.lastname: Ohta
authors.forename: Masayuki
authors.initials: M
authors.lastname: Yamamoto
mesh_terms: D000205:Actomyosin / Q000378:metabolism; D000595:Amino Acid Sequence; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002455:Cell Division; D018118:Chloride Channels / Q000378:metabolism*; D003001:Cloning, Molecular; D020662:Guanine Nucleotide Exchange Factors; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D012568:Schizosaccharomyces / Q000166:cytology / Q000378:metabolism; D029702:Schizosaccharomyces pombe Proteins; D017421:Sequence Analysis; D020798:Two-Hybrid System Techniques; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D018118:Chloride Channels; C089713:GEF1 protein, S cerevisiae; D020662:Guanine Nucleotide Exchange Factors; D011518:Proto-Oncogene Proteins; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; C089769:scd1 protein, S pombe; D000205:Actomyosin; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae