Kent N A, Tsang J S, Crowther D J, Mellor J
Department of Biochemistry, University of Oxford, United Kingdom.
Mol Cell Biol. 1994 Aug;14(8):5229-41. doi: 10.1128/mcb.14.8.5229-5241.1994.
CPF1 is an abundant basic-helix-loop-helix-ZIP protein that binds to the CDEI motif in Saccharomyces cerevisiae centromeres and in the promoters of numerous genes, including those encoding enzymes of the methionine biosynthetic pathway. Strains lacking CPF1 are methionine auxotrophs, and it has been proposed that CPF1 might positively influence transcription at the MET25 and MET16 genes by modulating promoter chromatin structure. We test this hypothesis and show that the regions surrounding the CDEI motifs in the MET25 and MET16 promoters are maintained in a nucleosome-free state and that this requires the entire CPF1 protein. However, the chromatin structure around the CDEI motifs does not change on derepression of transcription and does not correlate with the methionine phenotype of the cell. An intact CDEI motif but not CPF1 is required for transcriptional activation from a region of the MET25 upstream activation sequence. Our results suggest that CPF1 functions to modulate chromatin structure around the CDEI motif but that these changes at the MET25 and MET16 promoters do not explain how CPF1 functions to maintain methionine-independent growth. The presence of CPF1-dependent chromatin structures at these promoters leads to a weak repression of transcription.
CPF1是一种丰富的碱性螺旋-环-螺旋-拉链蛋白，它能与酿酒酵母着丝粒以及众多基因（包括那些编码甲硫氨酸生物合成途径中酶的基因）的启动子中的CDEI基序结合。缺乏CPF1的菌株是甲硫氨酸营养缺陷型，有人提出CPF1可能通过调节启动子染色质结构对MET25和MET16基因的转录产生正向影响。我们对这一假设进行了验证，结果表明MET25和MET16启动子中CDEI基序周围的区域保持无核小体状态，且这需要完整的CPF1蛋白。然而，CDEI基序周围的染色质结构在转录去阻遏时并未改变，且与细胞的甲硫氨酸表型无关。来自MET25上游激活序列区域的转录激活需要完整的CDEI基序而非CPF1。我们的结果表明，CPF1的功能是调节CDEI基序周围的染色质结构，但MET25和MET16启动子处的这些变化并不能解释CPF1如何发挥作用以维持不依赖甲硫氨酸的生长。这些启动子处存在依赖CPF1的染色质结构会导致转录受到微弱抑制。
