The UGG Isoacceptor of tRNAPro Is Naturally Prone to Frameshifts.
The UGG Isoacceptor of tRNAPro Is Naturally Prone to Frameshifts.
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DOI：
10.3390/ijms160714866
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发表时间：
2015-07-01
影响因子：
5.6
通讯作者：
Hou YM
中科院分区：
文献类型：
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作者：
Gamper HB;Masuda I;Frenkel-Morgenstern M;Hou YM
天然 tRNA 通常包含对摆动位置的转录后修饰，以扩大读取遗传密码的能力。其中一些修饰，由于能够在摆动位置赋予不完美的密码子-反密码子配对，可以诱导 tRNA 转变为替代阅读框的高度倾向。一个例子是大肠杆菌 tRNAPro 的天然 UGG 同工受体，其摆动核苷酸 U34 被转录后修饰为 cmo5U34，以读取所有四个脯氨酸密码子（5ʹ-CCA、5ʹ-CCC、5ʹ-CCG 和 5ʹ-CCU）。由于修饰的反密码子与 CCC 密码子的配对相对于 CCA 和 CCG 密码子而言特别弱，因此该 tRNA 可以轻松转移到滑溜的 mRNA 序列 CCC-CG 上的 +1 和 +2 框。我们表明，由于摆动位置密码子-反密码子配对的更高稳定性，向 +2 框架的转变更占主导地位。动力学分析表明，这两种类型的转变都可能发生在易位后复合物中 tRNA 停滞期间或从 A 位点易位到 P 位点期间。重要的是，虽然+1-框架后复合物对于肽基转移具有活性，但+2-框架复合物是较差的肽基供体。结合我们最近的工作，我们对+1和+2移码进行了机制上的区别，表明虽然+1移码被反密码子环中额外的转录后修饰的m1G37核苷酸抑制，但+2移码被核糖体抑制，支持核糖体在阅读框维护的整体质量控制中的作用。
Native tRNAs often contain post-transcriptional modifications to the wobble position to expand the capacity of reading the genetic code. Some of these modifications, due to the ability to confer imperfect codon-anticodon pairing at the wobble position, can induce a high propensity for tRNA to shift into alternative reading frames. An example is the native UGG isoacceptor of E. coli tRNAPro whose wobble nucleotide U34 is post-transcriptionally modified to cmo5U34 to read all four proline codons (5ʹ-CCA, 5ʹ-CCC, 5ʹ-CCG, and 5ʹ-CCU). Because the pairing of the modified anticodon to CCC codon is particularly weak relative to CCA and CCG codons, this tRNA can readily shift into both the +1 and +2-frame on the slippery mRNA sequence CCC-CG. We show that the shift to the +2-frame is more dominant, driven by the higher stability of the codon-anticodon pairing at the wobble position. Kinetic analysis suggests that both types of shifts can occur during stalling of the tRNA in a post-translocation complex or during translocation from the A to the P-site. Importantly, while the +1-frame post complex is active for peptidyl transfer, the +2-frame complex is a poor peptidyl donor. Together with our recent work, we draw a mechanistic distinction between +1 and +2-frameshifts, showing that while the +1-shifts are suppressed by the additional post-transcriptionally modified m1G37 nucleotide in the anticodon loop, the +2-shifts are suppressed by the ribosome, supporting a role of the ribosome in the overall quality control of reading-frame maintenance.