四种植物25S rRNA sarcin/ricin结构域甲基化核苷的分析

应用不同浓度的dNTP逆转录反应，分析丁苦瓜、丝瓜、蓖麻和水稻的25SrRNA sarcin/ricin区域中的甲基化核苷，发现了这4种植物25SrRNA的第3023、2966和2962位的腺嘌呤、胸腺嘧啶和腺嘌呤是2’-0-甲基化核苷；在丝瓜和苦瓜25SrRNA的第2992、2990位的胞嘧啶和鸟嘿吟是葫芦科植物所特有的两个2’-0—甲基化核苷；第2994位点的尿嘧啶是苦瓜、丝瓜、蓖麻和水稻的一个碱基甲基化核苷；而且，植物25SrRNA第3023位甲基化腺嘌呤核苷刚好位于sarcin/ricin结构域的茎环上，与核糖体失活蛋白切割位点相距仅5个核苷酸，而在哺乳动物和酵母的rRNA相同位点上没有甲基化修饰的存在，根据这一结果推测，RIPS来源植物核糖体RNA的自我保护可能与这一位点的修饰有关。

Determination of the Methylated Nucleotides in Sarcin/Ricin Domain and Its Flanked Sequences of 25S rRNA from Four Plants

Using primer extension at different dNTP concentrations the methylated nucleotides in sarcin/ricin domains and its flanked sequences of 25S rRNA were analyzed and determined from Oryza sativa, Momordica charantia, Luffa cylindrica and Ricinus communis. A3023, U2966 and A2962 were 2'-O-ribose methylated nucleotides and U2944 was base methylation modification in 25S rRNA of those four plants. C2992 and G2990 were two sites of 2'-O-ribose methylation only found in Momordica charantia and Luffa cylindrica. Interestingly, A3023 was located at sarcin/ricin loop of plant 25S rRNA. However, the site was 5 nucleotides down stream from a-sarcin/ricin cleavage site and unmethylated in mammals and S. cerevisiae rRNAs. The results suggest that the methylation modification in sarcin/ricin loop of plant rRNAs prevent the recognition and hydrolysis from the ribosome inactivating proteins.