A putative cyclic peptide efflux pump encoded by the TOXA gene of the plant-pathogenic fungus Cochliobolus carbonum
A putative cyclic peptide efflux pump encoded by the TOXA gene of the plant-pathogenic fungus Cochliobolus carbonum
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DOI：
10.1099/13500872-142-6-1557
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发表时间：
1996-06-01
期刊：
影响因子：
--
通讯作者：
Walton, JD
中科院分区：
文献类型：
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作者：
Pitkin, JW;Panaccione, DG;Walton, JD
由于产生一种宿主选择性环四肽，即hc -毒素，1种碳锥虫对某些玉米品系具有致病性。在编码hc -毒素生物合成中心酶的HTS1基因的两侧，发现了一个被命名为TOXA的基因。与HTS1一样，弓形虫病仅发生在产生hc毒素的真菌分离株中，并且在大多数产生毒素的分离株中以两个相连的拷贝存在。HTS1和TOXA转录方向相反，转录起始位点相距386 bp。预测产物为58 kDa的疏水蛋白，具有10-13个跨膜区。该序列与对四环素、甲氧基霉素和其他抗生素产生耐药性的主要促进剂超家族的几个成员高度相似。虽然有可能通过靶向基因破坏使TOXA的一个拷贝或另一个拷贝发生突变，但在单个菌株中多次尝试破坏两个拷贝都是不成功的，这表明TOXA是合成hc -毒素的菌株中必不可少的基因。基于其仅存在于产生hc毒素的菌株中，其与HTS1的接近性及其预测的氨基酸序列，我们提出TOXA编码一个hc毒素外排泵，该泵有助于自我保护hc毒素和/或将hc毒素分泌到细胞外环境中。
Race 1 isolates of Cochliobolus carbonum are pathogenic on certain maize lines due to production of a host-selective cyclic tetrapeptide, HC-toxin. Flanking HTS1, which encodes the central enzyme in HC-toxin biosynthesis, a gene was identified and named TOXA. Like HTS1, TOXA occurred only in isolates of the fungus that make HC-toxin and was present as two linked copies in most toxin-producing isolates. HTS1 and TOXA were transcribed in the opposite orientation and their transcriptional start sites were 386 bp apart. The predicted product of TOXA was a 58 kDa hydrophobic protein with 10-13 membrane-spanning regions. The sequence was highly similar to several members of the major facilitator superfamily that confer resistance to tetracycline, methylenomycin, and other antibiotics. Although it was possible to mutate one copy or the other of TOXA by targeted gene disruption, numerous attempts to disrupt both copies in a single strain were unsuccessful, suggesting that TOXA is an essential gene in strains that synthesize HC-toxin. On the basis of its presence only in HC-toxin-producing strains, its proximity to HTS1 and its predicted amino acid sequence, we propose that TOXA encodes an HC-toxin efflux pump which contributes to self-protection against HC-toxin and/or the secretion of HC-toxin into the extracellular milieu.