Kaneko I, Katsuya S, Tsuge T
Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Japan.
Gene. 1997 Dec 5;203(1):51-7. doi: 10.1016/s0378-1119(97)00490-3.
The circular DNA plasmid, designated pAAT56, has been isolated from strain T88-56 of the Japanese pear pathotype of Alternaria alternata. We determined the complete nucleotide sequence (5354 bp) of pAAT56 and mapped its possible open reading frames (ORFs). Three long ORFs, ORF1 (1290 bp), ORF2 (1653 bp) and ORF3 (690 bp), and four smaller ORFs, ORF4 to ORF7 (> or = 300 bp), were predicted from the sequence. The potential peptides derived from the ORFs other than ORF2 show no homology to other known proteins from a database search. However, ORF2 has significant homology to the pol gene of retrotransposons. The polypeptide derived from ORF2 includes sequences homologous to the reverse transcriptase (RT) and ribonuclease H (RNase H) domains of the retrotransposon Pol peptide. Phylogenetic comparison of RT domains from the retroelements placed pAAT56 in the Ty3/gypsy group of long terminal repeat (LTR) retrotransposons, most closely linked with those of filamentous fungi. The PCR primers were designed on the basis of nucleotide sequences encoding the highly-conserved amino-acid sequences in RT domains among pAAT56 and fungal retrotransposons. The PCR amplified the DNA fragments that possibly encode RT from strains of filamentous fungi that have been reported to carry retrotransposons. These results suggest that pAAT56 has acquired the pol gene from a Ty3/gypsy-group retrotransposon.
环状DNA质粒，命名为pAAT56，是从链格孢日本梨致病型菌株T88 - 56中分离得到的。我们测定了pAAT56的完整核苷酸序列（5354 bp），并对其可能的开放阅读框（ORF）进行了定位。从该序列预测出三个长开放阅读框，即ORF1（1290 bp）、ORF2（1653 bp）和ORF3（690 bp），以及四个较小的开放阅读框，即ORF4至ORF7（≥300 bp）。数据库搜索结果显示，除ORF2外，其他开放阅读框衍生的潜在肽段与其他已知蛋白质无同源性。然而，ORF2与逆转录转座子的pol基因具有显著同源性。ORF2衍生的多肽包含与逆转录转座子Pol肽的逆转录酶（RT）和核糖核酸酶H（RNase H）结构域同源的序列。对逆转录元件RT结构域的系统发育比较将pAAT56置于长末端重复序列（LTR）逆转录转座子的Ty3/gypsy组中，与丝状真菌的关系最为密切。根据pAAT56和真菌逆转录转座子中RT结构域编码高度保守氨基酸序列的核苷酸序列设计了PCR引物。PCR扩增出了可能编码已报道携带逆转录转座子的丝状真菌菌株RT的DNA片段。这些结果表明，pAAT56从一个Ty3/gypsy组逆转录转座子中获得了pol基因。
