Hamann A, Feller F, Osiewacz H D
Botanisches Institut, Biozentrum, J.W. Goethe-Universität, Frankfurt, Germany.
Mol Gen Genet. 2000 Jul;263(6):1061-9. doi: 10.1007/s004380050035.
A degenerate DNA transposon, Pat, was identified in the genomes of various wild-type strains of the filamentous fungus Podospora anserina. In these strains, the number (approximately 20-25 copies per genome) and location of Pat sequences appear to be conserved. Two copies of Pat, one complete and one partial, were cloned and characterized. The sequence of the complete element is 1856 bp long and contains imperfect inverted terminal repeats (ITRs) of 53 bp. The target site duplication comprises the sequence TA. The amino acid sequence derived from one reading frame of Pat shows significant homology to members of the Fot1 family of transposons. However, this reading frame is interrupted by numerous stop codons. Since no transcripts of Pat were identified in different P. anserina strains grown under standard conditions and under increased stress, we conclude that none of the copies of Pat is active in the strains analyzed, under the environmental conditions investigated. Comparison of the sequences of the two cloned Pat sequences revealed 89% (589/747 nucleotides) identity. Most of the differences (82%, 129/158) can be attributed to transitions preferentially at CpA:TpG and CpT:ApG dinucleotides. The dinucleotide ratios in Pat are similar to those in a Neurospora crassa transposon which was subject to repeat-induced mutation (RIP), but differ significantly from those found in single-copy genes of P. anserina and in fungal DNA transposons not modified by this mechanism. Molecular analysis of the progeny of a cross between the wild-type strain and a transgenic strain in which a nuclear gene was duplicated by transformation yielded the first clear evidence that a RIP-like process is active in P. anserina.
在丝状真菌粗糙脉孢菌的各种野生型菌株基因组中，鉴定出一种简并DNA转座子Pat。在这些菌株中，Pat序列的数量（每个基因组约20 - 25个拷贝）和位置似乎是保守的。克隆并表征了两个Pat拷贝，一个完整，一个部分。完整元件的序列长1856 bp，包含53 bp的不完全反向末端重复序列（ITR）。靶位点重复序列为TA。从Pat的一个阅读框推导的氨基酸序列与转座子Fot1家族成员显示出显著同源性。然而，这个阅读框被众多终止密码子打断。由于在标准条件下以及增加胁迫条件下生长的不同粗糙脉孢菌菌株中未鉴定到Pat的转录本，我们得出结论，在所研究的环境条件下，分析的菌株中没有一个Pat拷贝是活跃的。对两个克隆的Pat序列进行比较，发现其同一性为89%（589/747个核苷酸）。大多数差异（82%，129/158）可归因于优先在CpA:TpG和CpT:ApG二核苷酸处的转换。Pat中的二核苷酸比例与经历重复诱导突变（RIP）的粗糙脉孢菌转座子中的比例相似，但与粗糙脉孢菌单拷贝基因以及未受此机制修饰的真菌DNA转座子中的比例有显著差异。对野生型菌株和通过转化使一个核基因重复的转基因菌株杂交后代进行分子分析，首次明确证明了类似RIP的过程在粗糙脉孢菌中是活跃的。
