Hohn T M, Desjardins A E, McCormick S P
Mycotoxin Research Unit, USDA/ARS, National Center for Agricultural Utilization Research, Peoria, IL 61604, USA.
Mol Gen Genet. 1995 Jul 22;248(1):95-102. doi: 10.1007/BF02456618.
The Tri4 gene of Fusarium sporotrichioides was isolated from a cloned DNA fragment carrying the Tri5 gene by complementation of a Tri4- mutant. The nucleotide sequence of Tri4 was determined and the locations of three introns were identified. Analysis of Tri4 mRNA levels revealed that transcription reached maximum levels coincidently with the onset of trichothecene biosynthesis, and then declined 20-fold over the next 8 h. Disruption of Tri4 resulted in the loss of production of both trichothecenes and apotrichodiol and the accumulation of the unoxygenated pathway intermediate trichodiene. Transformants lacking a functional Tri4 gene were able to convert isotrichotriol, an early pathway intermediate, to T-2 toxin suggesting that most pathway enzymes are present in Tri4- mutants. These data suggest that the enzyme encoded by Tri4 catalyzes the first oxygenation step in the trichothecene pathway and participates in apotrichodiol biosynthesis. Tri4 encodes a protein of 520 residues (M(r) = 59 056) that shows significant homology with members of the superfamily of cytochromes P450. It appears most similar to the CYP3A subfamily (24.6% amino acid identity). Because it contains less than 40% positional identity with other cytochromes P450, the Tri4 gene has been placed in a new cytochrome P450 gene family designated CY P58.
通过对Tri4突变体进行互补，从携带Tri5基因的克隆DNA片段中分离出了拟枝孢镰刀菌的Tri4基因。测定了Tri4的核苷酸序列，并确定了三个内含子的位置。对Tri4 mRNA水平的分析表明，转录在单端孢霉烯生物合成开始时达到最高水平，然后在接下来的8小时内下降了20倍。Tri4的破坏导致单端孢霉烯和阿波单端孢二醇的产量丧失以及未氧化途径中间体单端孢菌烯的积累。缺乏功能性Tri4基因的转化体能够将早期途径中间体异单端孢三醇转化为T-2毒素，这表明Tri4突变体中存在大多数途径酶。这些数据表明，Tri4编码的酶催化单端孢霉烯途径中的第一步氧化反应，并参与阿波单端孢二醇的生物合成。Tri4编码一个由520个残基组成的蛋白质（分子量=59056），与细胞色素P450超家族成员具有显著同源性。它似乎与CYP3A亚家族最为相似（氨基酸同一性为24.6%）。由于它与其他细胞色素P450的位置同一性低于40%，Tri4基因已被归入一个新的细胞色素P450基因家族，命名为CYP58。
