Ramage L, Junne T, Hahne K, Lithgow T, Schatz G
Biocenter, University of Basel, Switzerland.
EMBO J. 1993 Nov;12(11):4115-23. doi: 10.1002/j.1460-2075.1993.tb06095.x.
We have identified a 20 kDa yeast mitochondrial outer membrane protein (termed MAS20) which appears to function as a protein import receptor. We cloned, sequenced and physically mapped the MAS20 gene and found that the protein is homologous to the MOM19 import receptor from Neurospora crassa. MAS20 and MOM19 contain the sequence motif F-X-K-A-L-X-V/L, which is repeated several times with minor variations in the MAS70/MOM72 receptors. To determine how MAS20 functions together with the previously identified yeast receptor MAS70, we constructed yeast mutants lacking either one or both of the receptors. Deletion of either receptor alone had little or no effect on fermentative growth and only partially inhibited mitochondrial protein import in vivo. Deletion of both receptors was lethal. Deleting only MAS70 did not affect respiration; deleting only MAS20 caused loss of respiration, but respiration could be restored by overexpressing MAS70. Import of the F1-ATPase beta-subunit into isolated mitochondria was only partly inhibited by IgGs against either MAS20 or MAS70, but both IgGs inhibited import completely. We conclude that the two receptors have overlapping specificities for mitochondrial precursor proteins and that neither receptor is by itself essential.
我们鉴定出一种20 kDa的酵母线粒体外膜蛋白（称为MAS20），它似乎作为一种蛋白质输入受体发挥作用。我们克隆、测序并对MAS20基因进行了物理定位，发现该蛋白与粗糙脉孢菌的MOM19输入受体同源。MAS20和MOM19含有序列基序F-X-K-A-L-X-V/L，该基序在MAS70/MOM72受体中重复出现几次，略有变化。为了确定MAS20如何与先前鉴定的酵母受体MAS70共同发挥作用，我们构建了缺失其中一种或两种受体的酵母突变体。单独缺失任何一种受体对发酵生长几乎没有影响，并且仅在体内部分抑制线粒体蛋白质输入。缺失两种受体是致死的。仅缺失MAS70不影响呼吸作用；仅缺失MAS20导致呼吸作用丧失，但通过过表达MAS70可恢复呼吸作用。针对MAS20或MAS70的IgG仅部分抑制F1-ATPaseβ亚基导入分离线粒体，但两种IgG均完全抑制导入。我们得出结论，这两种受体对线粒体前体蛋白具有重叠的特异性，并且任何一种受体本身都不是必需的。
