Dick F A, Karamanou S, Trumpower B L
Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
J Biol Chem. 1997 May 16;272(20):13372-9. doi: 10.1074/jbc.272.20.13372.
QSR1 (quinol-cytochrome c reductase subunit-requiring) is a highly conserved, essential gene in Saccharomyces cerevisiae that was identified through a synthetic lethal screen by its genetic relationship to QCR6, the gene for subunit 6 (Qcr6p) of the mitochondrial cytochrome bc1 complex. The function of the QSR1-encoded protein (Qsr1p) and its relationship to the QCR6-encoded protein are unknown. When yeast cell lysates are fractionated by density gradient centrifugation, Qsr1p separates from organelles and sediments with a uniformly sized population of particles that are similar to eukaryotic ribosomes upon velocity gradient centrifugation. When 40 S and 60 S ribosomal subunits are separated on velocity gradients, Qsr1p is found exclusively with the 60 S subunits, where it is a stoichiometric component. Extracts prepared from qsr1-1 cells are defective in in vitro translation assays relative to the wild type. In yeast cell lysates in which QCR6 rescues an otherwise lethal qsr1-1 mutation, Qcr6p is found only in mitochondria, both in respiratory-competent cells and in rho0 cells in which the bc1 complex is no longer present. These results suggest that suppression of the qsr1-1 mutation by QCR6 occurs by a trans-relationship across the outer mitochondrial membrane.
QSR1(需要喹啉 - 细胞色素c还原酶亚基)是酿酒酵母中一个高度保守的必需基因,它是通过合成致死筛选,根据其与线粒体细胞色素bc1复合体亚基6(Qcr6p)的基因QCR6的遗传关系而鉴定出来的。QSR1编码蛋白(Qsr1p)的功能及其与QCR6编码蛋白的关系尚不清楚。当酵母细胞裂解物通过密度梯度离心进行分级分离时,Qsr1p与细胞器分离,并在速度梯度离心时与一群大小均匀的颗粒一起沉淀,这些颗粒类似于真核核糖体。当40S和60S核糖体亚基在速度梯度上分离时,Qsr1p仅与60S亚基一起被发现,并且它是化学计量组分。相对于野生型,从qsr1 - 1细胞制备的提取物在体外翻译测定中存在缺陷。在QCR6挽救原本致死的qsr1 - 1突变的酵母细胞裂解物中,无论是在具有呼吸能力的细胞还是在不再存在bc1复合体的rho0细胞中,Qcr6p仅存在于线粒体中。这些结果表明,QCR6对qsr1 - 1突变的抑制是通过跨线粒体外膜的反式关系发生的。