Foiani M, Nadjar-Boger E, Capone R, Sagee S, Hashimshoni T, Kassir Y
Dipartimento di Genetica e di Biologia dei Microrganismi, Università degli Studi di Milano, Italy.
Mol Gen Genet. 1996 Dec 13;253(3):278-88. doi: 10.1007/s004380050323.
In this report we study the regulation of premeiotic DNA synthesis in Saccharomyces cerevisiae. DNA replication was monitored by fluorescence-activated cell sorting analysis and by analyzing the pattern of expression of the DNA polymerase alpha-primase complex. Wild-type cells and cells lacking one of the two principal regulators of meiosis, Ime1 and Ime2, were compared. We show that premeiotic DNA synthesis does not occur in ime1 delta diploids, but does occur in ime2 delta diploids with an 8-9 h delay. At late meiotic times, ime2 delta diploids exhibit an additional round of DNA synthesis. Furthermore, we show that in wild-type cells the B-subunit of DNA polymerase alpha is phosphorylated during premeiotic DNA synthesis, a phenomenon that has previously been reported for the mitotic cell cycle. Moreover, the catalytic subunit and the B-subunit of DNA polymerase alpha are specifically degraded during spore formation. Phosphorylation of the B-subunit does not occur in ime1 delta diploids, but does occur in ime2 delta diploids with an 8-9 h delay. In addition, we show that Ime2 is not absolutely required for commitment to meiotic recombination, spindle formation and nuclear division, although it is required for spore formation.
在本报告中，我们研究了酿酒酵母减数分裂前DNA合成的调控。通过荧光激活细胞分选分析以及分析DNA聚合酶α-引发酶复合物的表达模式来监测DNA复制。我们比较了野生型细胞和缺乏减数分裂两个主要调控因子之一Ime1和Ime2的细胞。我们发现，在ime1Δ二倍体细胞中不发生减数分裂前DNA合成，但在ime2Δ二倍体细胞中会发生，不过会延迟8 - 9小时。在减数分裂后期，ime2Δ二倍体细胞会出现额外一轮DNA合成。此外，我们表明，在野生型细胞中，DNA聚合酶α的B亚基在减数分裂前DNA合成过程中会发生磷酸化，这一现象先前在有丝分裂细胞周期中已有报道。而且，在孢子形成过程中，DNA聚合酶α的催化亚基和B亚基会被特异性降解。B亚基的磷酸化在ime1Δ二倍体细胞中不会发生，但在ime2Δ二倍体细胞中会发生，且延迟8 - 9小时。另外，我们表明，尽管Ime2是孢子形成所必需的，但它对于减数分裂重组、纺锤体形成和核分裂的启动并非绝对必需。
