Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India.
Mol Microbiol. 2009 May;72(3):795-808. doi: 10.1111/j.1365-2958.2009.06685.x.
Ribosomal RNA (rRNA) contains a number of modified nucleosides in functionally important regions including the intersubunit bridge regions. As the activity of ribosome recycling factor (RRF) in separating the large and the small subunits of the ribosome involves disruption of intersubunit bridges, we investigated the impact of rRNA methylations on ribosome recycling. We show that deficiency of rRNA methylations, especially at positions 1518 and 1519 of 16S rRNA near the interface with the 50S subunit and in the vicinity of the IF3 binding site, adversely affects the efficiency of RRF-mediated ribosome recycling. In addition, we show that a compromise in the RRF activity affords increased initiation with a mutant tRNA(fMet) wherein the three consecutive G-C base pairs ((29)GGG(31):(39)CCC(41)), a highly conserved feature of the initiator tRNAs, were mutated to those found in the elongator tRNA(Met) ((29)UCA(31):(39)ψGA(41)). This observation has allowed us to uncover a new role of RRF as a factor that contributes to fidelity of initiator tRNA selection on the ribosome. We discuss these and earlier findings to propose that RRF plays a crucial role during all the steps of protein synthesis.
核糖体 RNA（rRNA）在功能重要的区域包含许多修饰的核苷，包括亚基间桥区域。由于核糖体回收因子（RRF）在分离核糖体的大亚基和小亚基中的活性涉及到亚基间桥的破坏，我们研究了 rRNA 甲基化对核糖体回收的影响。我们表明，rRNA 甲基化的缺乏，特别是在 16S rRNA 的位置 1518 和 1519 附近，靠近与 50S 亚基的界面以及 IF3 结合位点附近，会对 RRF 介导的核糖体回收效率产生不利影响。此外，我们表明，RRF 活性的妥协为具有突变 tRNA(fMet)的起始提供了更高的效率，其中三个连续的 G-C 碱基对（（29）GGG（31）：（39）CCC（41）），是起始 tRNA 的高度保守特征，被突变为在延伸 tRNA(Met)中发现的那些（（29）UCA（31）：（39）ψGA（41））。这一观察结果使我们能够揭示 RRF 的一个新作用，即作为一种有助于核糖体上起始 tRNA 选择保真度的因素。我们讨论了这些和早期的发现，提出 RRF 在蛋白质合成的所有步骤中都起着至关重要的作用。
