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首页> 外文期刊>Journal of Molecular Biology >Specific and Non-specific Purine Trap in the T-loop of Normal and Suppressor tRNAs.
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Specific and Non-specific Purine Trap in the T-loop of Normal and Suppressor tRNAs.

机译：正常和抑制性tRNA的T环中的特异性和非特异性嘌呤陷阱。

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摘要

To elucidate the general constraints imposed on the structure of the D and T-loops in functional tRNAs, active suppressor tRNAs were selected in vivo from a combinatorial tRNA gene library in which several nucleotide positions in these loops were randomized. Analysis of the nucleotide sequences of the selected clones demonstrates that most of them contain combination U54-A58 allowing the formation of the standard reverse-Hoogsteen base-pair 54-58 in the T-loop. With only one exception, all these clones fall into two groups, each characterized by a distinct sequence pattern. Analysis of these two groups has allowed us to suggest two different types of nucleotide arrangement in the DT region. The first type, the so-called specific purine trap, is found in 12 individual tRNA clones and represents a generalized version of the standard D-T loop interaction. It consists of purine 18 sandwiched between the reverse-Hoogsteen base-pair U54-A58 and purine 57. The identity of purine 18 is restricted by the specific base-pairing with nucleotide 55. Depending on whether nucleotide 55 is U or G, purine 18 should be, respectively, G or A. The second structural type, the so-called non-specific purine trap, corresponds to the nucleotide sequence pattern found in 16 individual tRNA clones and is described here for the first time. It consists of purine 18 sandwiched between two reverse-Hoogsteen base-pairs U54-A58 and A55-C57 and, unlike the specific purine trap, requires the T-loop to contain an extra eighth nucleotide. Since purine 18 does not form a base-pair in the non-specific purine trap, both purines, G18 and A18, fit to the structure equally well. The important role of both the specific and non-specific purine traps in the formation of the tRNA L-shape is discussed.
机译：为了阐明对功能性tRNA的D和T环结构施加的一般限制，从组合的tRNA基因库中选择了体内活性抑制性tRNA，其中在这些环中的几个核苷酸位置是随机的。对所选克隆的核苷酸序列的分析表明，它们中的大多数都包含组合U54-A58，从而允许在T环中形成标准的反向Hoogsteen碱基对54-58。除了一个例外，所有这些克隆均分为两组，每组均具有不同的序列模式。对这两组的分析使我们能够提出DT区中两种不同类型的核苷酸排列。第一种类型，即所谓的特异性嘌呤阱，存在于12个单独的tRNA克隆中，代表标准D-T环相互作用的广义形式。它由夹在反向Hoogsteen碱基对U54-A58和嘌呤57之间的嘌呤18组成。嘌呤18的身份受与核苷酸55的特定碱基配对限制。嘌呤18取决于核苷酸55是U还是G。第二种结构类型，即所谓的非特异性嘌呤阱，对应于在16个单独的tRNA克隆中发现的核苷酸序列模式，在此首次进行描述。它由夹在两个反向Hoogsteen碱基对U54-A58和A55-C57之间的嘌呤18组成，与特定的嘌呤陷阱不同，它需要T环包含额外的第八个核苷酸。由于嘌呤18在非特异性嘌呤陷阱中不形成碱基对，因此，嘌呤G18和A18都同样适合该结构。讨论了特异性和非特异性嘌呤阱在tRNA L形形成中的重要作用。

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