Hering Oliver, Brenneis Mariam, Beer Jürgen, Suess Beatrix, Soppa Jörg
Goethe-University, Department of Biosciences, Biocentre, Institute for Molecular Biosciences, Max-von-Laue-Str. 9, D-60438 Frankfurt, Germany.
Mol Microbiol. 2009 Mar;71(6):1451-63. doi: 10.1111/j.1365-2958.2009.06615.x. Epub 2009 Jan 23.
Four different mechanisms for translation initiation are known, i.e. one prokaryotic mechanism involving a Shine-Dalgarno sequence, two eukaryotic mechanisms relying on ribosomal scanning or internal ribosomal entry sites, and one mechanism acting on leaderless transcripts. Recently it was reported that the majority of haloarchaeal transcripts is leaderless and that most leadered transcripts are devoid of a Shine-Dalgarno sequence, excluding the operation of a 'bacterial-like' initiation mechanism. Therefore, the current study concentrated on elucidating whether a 'eukaryotic-like' scanning mechanism might operate instead. GUG and UUG were efficiently used as start codons on leadered transcripts in vivo, in contrast to initiation on leaderless transcripts (and leadered eukaryotic transcripts). Deleted versions of the 5'-UTR initiated translation very inefficiently. Introduction of additional upstream AUGs did not influence the initiation efficiency at internal start codons. An additional in-frame AUG at the 5'-end led to the simultaneous usage of two start sites on the same message. A stable stem-loop structure at the 5'-end inhibited only initiation at the first AUG, but did not influence usage of the internal AUG. Taken together, operation of a scanning mechanism was excluded and the results indicate that a novel mechanism for translation initiation operates at least in haloarchaea.
已知有四种不同的翻译起始机制，即一种涉及Shine-Dalgarno序列的原核生物机制、两种依赖核糖体扫描或内部核糖体进入位点的真核生物机制，以及一种作用于无先导序列转录本的机制。最近有报道称，大多数嗜盐古菌转录本是无先导序列的，并且大多数有先导序列的转录本缺乏Shine-Dalgarno序列，排除了“类细菌”起始机制的运作。因此，当前的研究集中于阐明是否可能存在一种“类真核生物”的扫描机制。与在无先导序列转录本（以及有先导序列的真核生物转录本）上起始翻译相反，GUG和UUG在体内被有效地用作有先导序列转录本的起始密码子。5'-UTR的缺失版本起始翻译的效率非常低。额外上游AUG的引入并不影响内部起始密码子处的起始效率。5'-端一个额外的框内AUG导致在同一条信息上同时使用两个起始位点。5'-端的一个稳定茎环结构仅抑制第一个AUG处的起始，但不影响内部AUG的使用。综上所述，排除了扫描机制的运作，结果表明至少在嗜盐古菌中存在一种新的翻译起始机制。
