University of Michigan, Museum of Zoology, 1109 Geddes Ave, Ann Arbor, Michigan 48109-1079, USA.
BMC Genomics. 2009 Dec 11;10:598. doi: 10.1186/1471-2164-10-598.
Atypical tRNAs are functional minimal tRNAs, lacking either the D- or T-arm. They are significantly shorter than typical cloverleaf tRNAs. Widespread occurrence of atypical tRNAs was first demonstrated for secernentean nematodes and later in various arachnids. Evidence started to accumulate that tRNAs of certain acariform mites are even shorter than the minimal tRNAs of nematodes, raising the possibility that tRNAs lacking both D- and T-arms might exist in these organisms. The presence of cloverleaf tRNAs in acariform mites, particularly in the house dust mite genus Dermatophagoides, is still disputed.
Mitochondrial tRNAs of Dermatophagoides farinae are minimal, atypical tRNAs lacking either the T- or D-arm. The size (49-62, 54.4 +/- 2.86 nt) is significantly (p = 0.019) smaller than in Caenorhabditis elegans (53-63, 56.3 +/- 2.30 nt), a model minimal tRNA taxon. The shortest tRNA (49 nt) in Dermatophagoides is approaching the length of the shortest known tRNAs (45-49 nt) described in other acariform mites. The D-arm is absent in these tRNAs, and the inferred T-stem is small (2-3 bp) and thermodynamically unstable, suggesting that it may not exist in reality. The discriminator nucleotide is probably not encoded and is added postranscriptionally in many Dermatophagoides tRNAs.
Mitochondrial tRNAs of acariform mites are largely atypical, non-cloverleaf tRNAs. Among them, the shortest known tRNAs with no D-arm and a short and unstable T-arm can be inferred. While our study confirmed seven tRNAs in Dermatophagoides by limited EST data, further experimental evidence is needed to demonstrate extremely small and unusual tRNAs in acariform mites.
非典型 tRNA 是具有功能的最小 tRNA，缺少 D 臂或 T 臂。它们比典型的三叶形 tRNA 短得多。最早在分泌体线虫中发现了非典型 tRNA 的广泛存在，后来在各种蛛形纲动物中也发现了非典型 tRNA。有证据表明，某些蜱螨类螨的 tRNA 甚至比线虫的最小 tRNA 还要短，这增加了这些生物中可能存在既缺少 D 臂又缺少 T 臂的 tRNA 的可能性。在蜱螨类中存在三叶草形 tRNA，特别是在屋尘螨属的尘螨中，这一点仍有争议。
粉尘螨的线粒体 tRNA 是最小的、非典型的 tRNA，既缺少 T 臂又缺少 D 臂。大小（49-62，54.4 +/- 2.86 nt）明显小于秀丽隐杆线虫（53-63，56.3 +/- 2.30 nt）（p = 0.019），后者是最小的典型 tRNA 分类群。粉尘螨中最短的 tRNA（49 nt）接近其他蜱螨类中描述的最短已知 tRNA（45-49 nt）的长度。这些 tRNA 中没有 D 臂，推断的 T 茎很小（2-3 bp）且热力学不稳定，这表明它可能实际上不存在。区分核苷酸可能没有被编码，并在后转录过程中添加到许多粉尘螨的 tRNA 中。
蜱螨类的线粒体 tRNA 主要是非典型的非三叶草形 tRNA。其中，推断出了没有 D 臂和短而不稳定的 T 臂的最短已知 tRNA。虽然我们的研究通过有限的 EST 数据证实了粉尘螨中的 7 种 tRNA，但需要进一步的实验证据来证明蜱螨类中存在非常小且不寻常的 tRNA。
