Kaplan R, Hartstein E
J Biol Chem. 1976 Feb 25;251(4):1147-53.
An attempt was made, in starved Escherichia coli cells, to locate the site at which the process of ribosome degradation is initiated. Supernatant and rapidly sedimenting pellet fractions from exponentially growing and from carbon-starved cells were prepared, and the ribonucleic acids from these fractions were seperated by polyacrylamide electrophoresis and quantitated. The data indicated that 23 S, 16 S, and 5 S RNA are lost only from the pellet; and also that the low molecular weight RNA degradation products are confined to this fraction. Ribosomes from supernatant and pellet fractions were seperated on sucrose density gradients. The sedimentation profiles obtained indicated that pellet fractions of starved cells contain for the most part 50 S and 30 S subunits, whereas 70 S monosomes were most abundant in the supernatant fraction. In vitro measurements on RNA degradation in supernatant and rapidly sedimenting pellet fractions confirmed the in vivo data on the exclusive degradation of ribosomal RNA in the pellet. Based on these data and on previous observations, we suggest that the endoribonucleolytic attack which triggers ribosome degradation, occurs in free subunits attached to the rapidly sedimenting membrane fraction. Subsequently, the ribosome falls apart, and the small RNA pieces generated remain attached to the pellet fraction until their final degradation by the exonuclease.
在饥饿的大肠杆菌细胞中，人们试图确定核糖体降解过程起始的位点。制备了指数生长期细胞和碳饥饿细胞的上清液和快速沉降的沉淀部分，并通过聚丙烯酰胺电泳分离这些部分的核糖核酸并进行定量。数据表明，23S、16S和5S RNA仅从沉淀中丢失；而且低分子量RNA降解产物也局限于该部分。通过蔗糖密度梯度分离上清液和沉淀部分的核糖体。得到的沉降图谱表明，饥饿细胞的沉淀部分大部分含有50S和30S亚基，而70S单体在上清液部分中最为丰富。对上清液和快速沉降的沉淀部分中RNA降解的体外测量证实了体内关于沉淀中核糖体RNA特异性降解的数据。基于这些数据和先前的观察结果，我们认为引发核糖体降解的核糖核酸内切酶攻击发生在附着于快速沉降膜部分的游离亚基中。随后，核糖体解体，产生的小RNA片段仍附着于沉淀部分，直至被外切核酸酶最终降解。
