Endo Y, Wool I G
J Biol Chem. 1982 Aug 10;257(15):9054-60.
alpha-Sarcin is a cytotoxic protein that inhibits eukaryotic elongation factor 1 catalyzed binding of aminoacyl-tRNA to eukaryotic ribosomes as a result of cleaving a fragment from the large RNA in the 60 S ribosomal subunit. Rat liver polysomes are sensitive to alpha-sarcin in vitro only if the treatment is carried out in the presence of EDTA. The oligonucleotide produced by alpha-sarcin action on rat liver ribosomes is derived from the 3' end of 28 S rRNA and has a molecular weight of approximately 161,000 (about 488 bases). The sequence at the site of cleavage (the 5' end of the oligonucleotide produced by alpha-sarcin action on rat liver ribosomes) was AGGAAC for both rat liver 28 S rRNA and yeast 25 S rRNA. Based on the size of the alpha-fragment derived from Escherichia coli ribosomes (about 243 nucleotides), it is likely that a similar sequence, AGGACC, occurs at the site of cleavage of prokaryotic 23 S rRNA. It is also likely that the sequence on the 5' side of the alpha-sarcin cleavage site is UAGUACGAG. The sequence UAGUACGAGAGGAAC must be important because it is conserved and because hydrolysis of a single phosphodiester bond there inactivates the ribosome. We suggest that this region of the large nucleic acid in the 60 S subparticle is involved in binding aminoacyl-tRNA to the ribosome, first, because it is the eukaryotic elongation factor 1 catalyzed reaction that is inhibited by alpha-sarcin, and second, because peptidyl-tRNA seems to protect polysomes against the toxin. The function of EDTA appears to be to remove peptidyl-tRNA since puromycin also sensitizes polysomes to alpha-sarcin.
α-肌动蛋白是一种细胞毒性蛋白，它通过从60S核糖体亚基的大RNA上切割一个片段，抑制真核延伸因子1催化的氨酰基-tRNA与真核核糖体的结合。大鼠肝脏多核糖体在体外仅在EDTA存在的情况下对α-肌动蛋白敏感。α-肌动蛋白作用于大鼠肝脏核糖体产生的寡核苷酸来自28S rRNA的3'端，分子量约为161,000（约488个碱基）。α-肌动蛋白作用于大鼠肝脏核糖体产生的寡核苷酸的切割位点（5'端）的序列，对于大鼠肝脏28S rRNA和酵母25S rRNA均为AGGAAC。基于源自大肠杆菌核糖体的α片段的大小（约243个核苷酸），原核23S rRNA的切割位点可能存在类似序列AGGACC。α-肌动蛋白切割位点5'侧的序列也可能是UAGUACGAG。序列UAGUACGAGAGGAAC一定很重要，因为它是保守的，并且在那里水解单个磷酸二酯键会使核糖体失活。我们认为，60S亚颗粒中大核酸的这个区域参与氨酰基-tRNA与核糖体的结合，首先是因为α-肌动蛋白抑制的是真核延伸因子1催化的反应，其次是因为肽基-tRNA似乎能保护多核糖体免受毒素侵害。EDTA的作用似乎是去除肽基-tRNA，因为嘌呤霉素也会使多核糖体对α-肌动蛋白敏感。
