核糖体移码
核糖体移码（Ribosomal frameshift）又称转译移码（Translational frameshift），是生物细胞中核糖体进行转译时，mRNA上的特定序列与二级结构使核糖体发生位移而破坏开放阅读框的现象[3]。由于mRNA上的密码子是由3个核苷酸对应一个氨基酸，+1、-1等核糖体移码会影响下游的开放阅读框，进而转译出完全不同的蛋白质[4]。核糖体移码可使一个mRNA得以转译出数种不同的蛋白质产物，此机制主要在病毒（反转录病毒[5]、劳斯肉瘤病毒（RSV）[1]、冠状病毒[6]、流感病毒[7]、反转录转座子等）的mRNA中发现，但也见于一些真核生物细胞基因的mRNA，可能为细胞调控基因表现的机制之一[8][9]。
最常见的核糖体移码为-1核糖体移码（programmed −1 ribosomal frameshifting, −1 PRF），此外还有较罕见的+1核糖体移码与-2核糖体移码[3]。发生-1核糖体移码的序列通常包含滑动序列、间隔序列（spacer）与茎环等三个元件，典型的滑动序列基序为X_XXY_YYH（X可为任意核苷酸、Y为A或U、H则为ACU三者之一），-1移码发生时，原与XXY密码子结合的核糖体P位点与其上的tRNA向前位移，改与XXX结合，同时原与YYH结合的A位点与其tRNA也改与YYY结合，新的反密码子/密码子配对除密码子三号位的核苷酸外，一号位与二号位的核苷酸皆与原本的相同[10]，而三号位因有摇摆碱基对，反密码子/密码子的结合力本就较弱，不对两者的结合造成严重影响[3][11]。
发生+1核糖体移码的序列则没有特定基序[2]，一般机制为使用一较罕见（对应tRNA的量较少）的密码子使转译发生停滞，增加核糖体发生移码的机会[2][12]。
参考文献
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