Obara-Ishihara T, Okayama H
Okayama Cell Switching Project, ERATO, JRDC, Kyoto, Japan.
EMBO J. 1994 Apr 15;13(8):1863-72. doi: 10.1002/j.1460-2075.1994.tb06455.x.
In the fission yeast Schizosaccharomyces pombe, the cdc10+/SWI family members constitute the cell cycle 'start' genes. res1+ and res2+ are the newly identified members of this family and encode putative association partners of the Cdc10 protein. The Pat1 kinase plays a pivotal role in switching between vegetative growth and sexual development, and its inactivation in haploid cells induces unconditional growth arrest and subsequent meiosis. We have identified as an extragenic suppressor of a temperature sensitive pat1-114 mutant, a new B-type cyclin that negatively regulates conjugation by interacting with these 'start' genes. This cyclin, named Cyc17, is highly homologous with Cdc13, but has no detectable activity as a mitotic cyclin. Deletion of cyc17+ markedly enhances conjugation, despite the presence of nitrogen source, and accelerates growth arrest in G1 upon nitrogen starvation. Conversely, overexpression of the cyc17+ gene strongly inhibits conjugation. The cyc17+ gene is transcribed into 3.2 kb poly(A)+ and 3.0 kb poly(A)- RNAs. Only the poly(A)+ species is expressed during vegetative growth and periodically with a peak in the G1 and S phases of the cell cycle. On the other hand, the poly(A)- transcript is highly induced during conjugation. This induction is lost in res2- cells, whereas the poly(A)+ transcript is significantly reduced in res1- cells. However, the mating inhibition as well as the ability to rescue the pat1 mutation by overexpression of res1+ and res2+ are totally abolished in cyc17- cells. Thus, in S.pombe, a B-type cyclin, regulated by the newly identified cell cycle 'start' genes, plays a crucial role in the control of sexual development.
在裂殖酵母粟酒裂殖酵母中，cdc10⁺/SWI家族成员构成细胞周期“起始”基因。res1⁺和res2⁺是该家族新鉴定的成员，编码Cdc10蛋白的假定结合伙伴。Pat1激酶在营养生长和有性发育之间的转换中起关键作用，其在单倍体细胞中的失活会导致无条件生长停滞和随后的减数分裂。我们已鉴定出一种新的B型细胞周期蛋白，它作为温度敏感型pat1 - 114突变体的基因外抑制子，通过与这些“起始”基因相互作用来负调控接合作用。这种细胞周期蛋白名为Cyc17，与Cdc13高度同源，但作为有丝分裂细胞周期蛋白没有可检测到的活性。cyc17⁺的缺失显著增强了接合作用，尽管存在氮源，并且在氮饥饿时加速了G1期的生长停滞。相反，cyc17⁺基因的过表达强烈抑制接合作用。cyc17⁺基因转录为3.2 kb的聚腺苷酸化（poly(A)⁺）和3.0 kb的非聚腺苷酸化（poly(A)⁻）RNA。只有poly(A)⁺物种在营养生长期间表达，并在细胞周期的G1期和S期周期性出现峰值。另一方面，poly(A)⁻转录本在接合期间被高度诱导。这种诱导在res2⁻细胞中消失，而poly(A)⁺转录本在res1⁻细胞中显著减少。然而，在cyc17⁻细胞中，接合抑制以及通过res1⁺和res2⁺过表达挽救pat1突变的能力完全丧失。因此，在粟酒裂殖酵母中，一种受新鉴定的细胞周期“起始”基因调控的B型细胞周期蛋白在有性发育的控制中起关键作用。
