Pedley K F, Walton J D
Department of Energy-Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA.
Proc Natl Acad Sci U S A. 2001 Nov 20;98(24):14174-9. doi: 10.1073/pnas.231491298. Epub 2001 Nov 6.
Strains of the filamentous fungus Cochliobolus carbonum that produce the host-selective compound HC-toxin, a cyclic tetrapeptide, are highly virulent on certain genotypes of maize (Zea mays L.). Production of HC-toxin is under the control of a complex locus, TOX2, which is composed of at least seven linked and duplicated genes that are present only in toxin-producing strains of C. carbonum. One of these genes, TOXE, was earlier shown to be required for the expression of the other TOX2 genes. TOXE has four ankyrin repeats and a basic region similar to those found in basic leucine zipper (bZIP) proteins, but lacks any apparent leucine zipper. Here we show that TOXE is a DNA-binding protein that recognizes a ten-base motif (the "tox-box") without dyad symmetry that is present in the promoters of all of the known TOX2 genes. Both the basic region and the ankyrin repeats are involved in DNA binding. A region of TOXE that includes the first ankyrin repeat is necessary and sufficient for transcriptional activation in yeast. The data indicate that TOXE is the prototype of a new family of transcription factor, so far found only in plant-pathogenic fungi. TOXE plays a specific regulatory role in HC-toxin production and, therefore, pathogenicity by C. carbonum.
能产生宿主选择性化合物HC毒素（一种环四肽）的丝状真菌玉米炭疽菌菌株，对某些基因型的玉米（Zea mays L.）具有高度毒性。HC毒素的产生受一个复杂基因座TOX2的控制，该基因座由至少七个连锁和重复的基因组成，这些基因仅存在于产毒素的玉米炭疽菌菌株中。这些基因之一TOXE，先前已证明它是其他TOX2基因表达所必需的。TOXE有四个锚蛋白重复序列和一个与碱性亮氨酸拉链（bZIP）蛋白中发现的类似的碱性区域，但缺乏明显的亮氨酸拉链。在这里，我们表明TOXE是一种DNA结合蛋白，它识别一个没有二元对称性的十碱基基序（“tox盒”），该基序存在于所有已知TOX2基因的启动子中。碱性区域和锚蛋白重复序列都参与DNA结合。TOXE中包含第一个锚蛋白重复序列的区域对于酵母中的转录激活是必要且充分的。数据表明TOXE是一个新的转录因子家族的原型，迄今为止仅在植物致病真菌中发现。TOXE在HC毒素产生以及因此在玉米炭疽菌的致病性中发挥特定的调节作用。
