Moll T, Schwob E, Koch C, Moore A, Auer H, Nasmyth K
Institute of Molecular Pathology, Vienna, Austria.
Philos Trans R Soc Lond B Biol Sci. 1993 Jun 29;340(1293):351-60. doi: 10.1098/rstb.1993.0078.
Unlike early embryonic cleavage divisions in certain animals, cell-cycle progression in yeast and probably also in all metazoan somatic cells requires the periodic transcriptional activation of certain key genes. Thus far, the only clear examples are genes that encode a class of unstable 'cyclin' proteins, which bind and activate the cdc2/Cdc28 protein kinase: the G1-specific cyclins encoded by CLN1 and CLN2, a B-type cyclin implicated in DNA replication encoded by CLB5; and four B-type cyclins involved in mitosis encoded by CLB1, 2, 3, 4. CLN1, CLN2, and CLB5 are transcribed in late G1, as cells undergo Start. A transcription factor composed of Swi4 and Swi6 proteins (called SBF) activates CLN1 and CLN2 transcription via a positive feedback loop in which Cln proteins activate their own transcription. A different but related transcription factor called MBF seems responsible for the late G1-specific transcription of most DNA replication genes including CLB5. We have purified MBF and shown that it contains Swi6 and a 110-120 kDa protein distinct from Swi4 (p120) that contacts DNA. Thus, we propose that SBF and MBF share a common regulatory subunit (Swi6) but recognize their promoter elements via distinct DNA binding subunits.
与某些动物早期胚胎卵裂不同，酵母以及可能所有后生动物体细胞中的细胞周期进程需要某些关键基因的周期性转录激活。到目前为止，唯一明确的例子是编码一类不稳定“细胞周期蛋白”的基因，这些蛋白结合并激活cdc2/Cdc28蛋白激酶：由CLN1和CLN2编码的G1特异性细胞周期蛋白、由CLB5编码的参与DNA复制的B型细胞周期蛋白；以及由CLB1、2、3、4编码的参与有丝分裂的四种B型细胞周期蛋白。CLN1、CLN2和CLB5在G1晚期转录，此时细胞进入起始点。由Swi4和Swi6蛋白组成的转录因子（称为SBF）通过正反馈环激活CLN1和CLN2转录，其中Cln蛋白激活它们自身的转录。一种不同但相关的转录因子称为MBF，似乎负责包括CLB5在内的大多数DNA复制基因的G1晚期特异性转录。我们已经纯化了MBF，并表明它含有Swi6和一种与Swi4不同的110 - 120 kDa蛋白质（p120），该蛋白质与DNA接触。因此，我们提出SBF和MBF共享一个共同的调节亚基（Swi6），但通过不同的DNA结合亚基识别它们的启动子元件。
