Garbarino Joan E, Gibbons I R
Molecular and Cell Biology Department, University of California Berkeley, 94720-3200, USA.
BMC Genomics. 2002 Jul 8;3:18. doi: 10.1186/1471-2164-3-18.
The largest open reading frame in the Saccharomyces genome encodes midasin (MDN1p, YLR106p), an AAA ATPase of 560 kDa that is essential for cell viability. Orthologs of midasin have been identified in the genome projects for Drosophila, Arabidopsis, and Schizosaccharomyces pombe.
Midasin is present as a single-copy gene encoding a well-conserved protein of approximately 600 kDa in all eukaryotes for which data are available. In humans, the gene maps to 6q15 and encodes a predicted protein of 5596 residues (632 kDa). Sequence alignments of midasin from humans, yeast, Giardia and Encephalitozoon indicate that its domain structure comprises an N-terminal domain (35 kDa), followed by an AAA domain containing six tandem AAA protomers (approximately 30 kDa each), a linker domain (260 kDa), an acidic domain (approximately 70 kDa) containing 35-40% aspartate and glutamate, and a carboxy-terminal M-domain (30 kDa) that possesses MIDAS sequence motifs and is homologous to the I-domain of integrins. Expression of hemagglutamin-tagged midasin in yeast demonstrates a polypeptide of the anticipated size that is localized principally in the nucleus.
The highly conserved structure of midasin in eukaryotes, taken in conjunction with its nuclear localization in yeast, suggests that midasin may function as a nuclear chaperone and be involved in the assembly/disassembly of macromolecular complexes in the nucleus. The AAA domain of midasin is evolutionarily related to that of dynein, but it appears to lack a microtubule-binding site.
酿酒酵母基因组中最大的开放阅读框编码中达辛（MDN1p，YLR106p），这是一种560 kDa的AAA型ATP酶，对细胞活力至关重要。在果蝇、拟南芥和粟酒裂殖酵母的基因组计划中已鉴定出中达辛的直系同源物。
在所有有数据的真核生物中，中达辛以单拷贝基因形式存在，编码一种约600 kDa的高度保守蛋白。在人类中，该基因定位于6q15，编码一个预测的含5596个残基（632 kDa）的蛋白。人类、酵母、贾第虫和脑胞内原虫的中达辛序列比对表明，其结构域结构包括一个N端结构域（35 kDa），接着是一个包含六个串联AAA原聚体的AAA结构域（每个约30 kDa）、一个连接结构域（260 kDa）、一个酸性结构域（约70 kDa），该酸性结构域含有35 - 40%的天冬氨酸和谷氨酸，以及一个羧基端M结构域（30 kDa），该结构域具有MIDAS序列基序且与整合素的I结构域同源。在酵母中表达血凝素标记的中达辛显示出预期大小的多肽，其主要定位于细胞核。
真核生物中中达辛的高度保守结构，结合其在酵母中的核定位，表明中达辛可能作为一种核伴侣发挥作用，并参与细胞核中大分子复合物的组装/拆卸。中达辛的AAA结构域在进化上与动力蛋白的AAA结构域相关，但它似乎缺乏微管结合位点。
