當(dāng)信使RNA（mRNA）被翻譯成蛋白時(shí),，蛋白編碼序列的末端由一個(gè)“三堿基”終止密碼子來指示,。終止密碼子不編碼氨基酸，但最近的研究表明,，將第一個(gè)堿基改為一個(gè)假尿苷（Ψ,，核苷尿苷的C-糖苷異構(gòu)體）將允許結(jié)合一個(gè)氨基酸，以使翻譯能夠越過終止密碼子繼續(xù)進(jìn)行,。Venki Ramakrishnan 及其同事確定了與一個(gè) mRNA 形成復(fù)合物的30S 核糖體亞單元的結(jié)構(gòu),，其中ΨAG在A點(diǎn)，并有一部分“絲氨酸轉(zhuǎn)移RNA”,。該結(jié)構(gòu)顯示了在該密碼子的第一個(gè)位置上的出乎意料的“嘌呤-嘌呤”堿基對(duì)以及在第二和第三個(gè)位置上的異常配對(duì),。這項(xiàng)研究為核糖體的解碼中心中的可塑性提供了新證據(jù)。
Nature doi:10.1038/nature12302
Unusual base pairing during the decoding of a stop codon by the ribosome
Israel S. Fernández, Chyan Leong Ng, Ann C. Kelley, Guowei Wu, Yi-Tao Yu & V. Ramakrishnan
During normal translation, the binding of a release factor to one of the three stop codons (UGA, UAA or UAG) results in the termination of protein synthesis. However, modification of the initial uridine to a pseudouridine (Ψ) allows efficient recognition and read-through of these stop codons by a transfer RNA (tRNA), although it requires the formation of two normally forbidden purine–purine base pairs1. Here we determined the crystal structure at 3.1 Å resolution of the 30S ribosomal subunit in complex with the anticodon stem loop of tRNASer bound to the ΨAG stop codon in the A site. The ΨA base pair at the first position is accompanied by the formation of purine–purine base pairs at the second and third positions of the codon, which show an unusual Watson–Crick/Hoogsteen geometry. The structure shows a previously unsuspected ability of the ribosomal decoding centre to accommodate non-canonical base pairs.
