Aleksenko A, Clutterbuck A J
Division of Molecular Genetics, University of Glasgow, UK.
Mol Microbiol. 1996 Feb;19(3):565-74. doi: 10.1046/j.1365-2958.1996.400937.x.
The AMA1 sequence was isolated from a genomic library of Aspergillus nidulans on the basis of its ability to enhance transformation frequency and generate phenotypically unstable transformants in this fungus. These properties were previously shown to be the result of extrachromosomal replication of AMA1-bearing plasmids. Here we demonstrate that AMA1 is an inverted duplication of a sequence which has other isolated genomic copies. These sequences (mobile Aspergillus transformation enhancers, or MATEs) share a high degree of sequence similarity and exhibit some features characteristic of mobile elements, including a potential Met-tRNA priming site, similar to that found in retrotransposons of the Ty-copia group. The nucleotide sequence does not encode any extended polypeptides but contains ARS-consensus matches and a multiply repeated 'Spe' motif, which may be described as a symmetrically duplicated topoisomerase I recognition site. This motif was shown to be a target for illegitimate recombination events. The mobility of members of the MATE family is inferred from the observation that their chromosomal locations are highly variable between wild Aspergillus isolates. The inverted duplication AMA1 is present in laboratory strains derived from the Glasgow isolate but not in other wild isolates tested. This indicates that the inverted duplication AMA1 is of recent evolutionary origin and probably does not exert any conserved function in the chromosome. We discuss possible connections between structural features of AMA1 and its ability to promote extrachromosomal plasmid replication.
AMA1序列是从构巢曲霉的基因组文库中分离出来的，其依据是它能够提高转化频率并在这种真菌中产生表型不稳定的转化体。这些特性先前已被证明是携带AMA1的质粒染色体外复制的结果。在这里，我们证明AMA1是一个序列的反向重复，该序列还有其他分离的基因组拷贝。这些序列（移动曲霉转化增强子，或MATEs）具有高度的序列相似性，并表现出一些移动元件的特征，包括一个潜在的Met-tRNA引物位点，类似于在Ty-copia组反转录转座子中发现的位点。核苷酸序列不编码任何延伸的多肽，但包含ARS一致匹配序列和一个多次重复的“Spe”基序，该基序可被描述为对称重复的拓扑异构酶I识别位点。该基序被证明是非法重组事件的靶点。MATE家族成员的移动性是从以下观察结果推断出来的：它们在野生曲霉分离株之间的染色体位置高度可变。反向重复AMA1存在于源自格拉斯哥分离株的实验室菌株中，但在测试的其他野生分离株中不存在。这表明反向重复AMA1是近期进化起源的，可能在染色体中不发挥任何保守功能。我们讨论了AMA1的结构特征与其促进染色体外质粒复制能力之间的可能联系。
