Ogas J, Andrews B J, Herskowitz I
Department of Biochemistry and Biophysics, University of California, San Francisco 94143-0448.
Cell. 1991 Sep 6;66(5):1015-26. doi: 10.1016/0092-8674(91)90445-5.
SWI4 of budding yeast codes for a component of a transcription factor (cell cycle box factor, or CCBF) necessary for G1-specific expression of HO. We show that SWI4 is essential for haploid cell viability at high temperature and in a/alpha cells at all temperatures: SWI4-deficient cells arrest as large unbudded cells. Eight high copy number plasmids were identified that allow swi4- strains to grow under nonpermissive conditions. Two carry G1 cyclin genes, CLN1 and CLN2; another carries HCS26, coding for a putative cyclin, a/alpha swi4- mutants exhibit 3- to 20-fold reductions in the levels of CLN1, CLN2, and HCS26 transcripts. The requirement of SWI4 for transcription appears to be direct: each gene contains sites similar to the CCBF-binding site; CCBF binds to the upstream region of HCS26. We propose that SWI4 participates in a positive feedback loop by which CLN1, CLN2, and possibly HCS26 promote their own transcription in G1.
芽殖酵母的SWI4编码一种转录因子（细胞周期盒因子，即CCBF）的组成成分，该转录因子是HO基因G1期特异性表达所必需的。我们发现，SWI4对于单倍体细胞在高温下以及a/α细胞在所有温度下的生存能力至关重要：缺乏SWI4的细胞会停滞成为未出芽的大细胞。我们鉴定出了八个高拷贝数质粒，它们能使swi4-菌株在非允许条件下生长。其中两个携带G1期细胞周期蛋白基因CLN1和CLN2；另一个携带HCS26，其编码一种假定的细胞周期蛋白，a/α swi4-突变体中CLN1、CLN2和HCS26转录本水平降低了3至20倍。SWI4对转录的需求似乎是直接的：每个基因都含有与CCBF结合位点相似的序列；CCBF能结合到HCS26的上游区域。我们提出，SWI4参与了一个正反馈环，通过这个反馈环，CLN1、CLN2以及可能的HCS26在G1期促进自身的转录。
