Beagley C T, Okimoto R, Wolstenholme D R
Department of Biology, University of Utah, Salt Lake City, Utah 84112, USA.
Genetics. 1999 Jun;152(2):641-52. doi: 10.1093/genetics/152.2.641.
A 2500-nucleotide pair (ntp) sequence of F-type mitochondrial (mt) DNA of the Pacific Rim mussel Mytilus californianus (class Bivalvia, phylum Mollusca) that contains two complete (ND2 and ND3) and two partial (COI and COIII) protein genes and nine tRNA genes is presented. Seven of the encoded tRNAs (Ala, Arg, His, Met(AUA), Pro, Ser(UCN), and Trp) have the potential to fold into the orthodox four-armed tRNA secondary structure, while two [tRNASer(AGN) and a second tRNASer(UCN)] will fold only into tRNAs with a dihydrouridine (DHU) arm-replacement loop. Comparison of these mt-tRNA gene sequences with previously published, corresponding M. edulis F-type mtDNA indicates that similarity between the four-armed tRNASer(UCN) genes is only 63.8% compared with an average of 92.1% (range 86.2-98. 5%) for the remaining eight tRNA genes. Northern blot analysis indicated that mature tRNAs encoded by the DHU arm-replacement loop-containing tRNASer(UCN), tRNASer(AGN), tRNAMet(AUA), tRNATrp, and tRNAPro genes occur in M. californianus mitochondria, strengthening the view that all of these genes are functional. However, Northern blot and 5' RACE (rapid amplification of cDNA ends) analyses indicated that the four-armed tRNASer(UCN) gene is transcribed into a stable RNA that includes the downstream COI sequence and is not processed into a mature tRNA. On the basis of these observations the M. californianus and M. edulis four-armed tRNASer(UCN) sequences are interpreted as pseudo-tRNASer(UCN) genes.
本文展示了太平洋沿岸贻贝加州贻贝（双壳纲，软体动物门）F型线粒体（mt）DNA的一段2500个核苷酸对（ntp）的序列，该序列包含两个完整的（ND2和ND3）和两个部分的（COI和COIII）蛋白质基因以及九个tRNA基因。其中七个编码的tRNA（丙氨酸、精氨酸、组氨酸、甲硫氨酸（AUA）、脯氨酸、丝氨酸（UCN）和色氨酸）有可能折叠成传统的四臂tRNA二级结构，而另外两个[tRNASer(AGN)和第二个tRNASer(UCN)]只会折叠成具有二氢尿嘧啶（DHU）臂替代环的tRNA。将这些mt-tRNA基因序列与先前发表的相应的紫贻贝F型mtDNA进行比较表明，四臂tRNASer(UCN)基因之间的相似性仅为63.8%，而其余八个tRNA基因的平均相似性为92.1%（范围为86.2 - 98.5%）。Northern印迹分析表明，由包含DHU臂替代环的tRNASer(UCN)、tRNASer(AGN)、tRNAMet(AUA)、tRNATrp和tRNAPro基因编码的成熟tRNA存在于加州贻贝线粒体中，这强化了所有这些基因都具有功能的观点。然而，Northern印迹和5' RACE（cDNA末端快速扩增）分析表明，四臂tRNASer(UCN)基因转录成一种稳定的RNA，该RNA包括下游的COI序列，并且不会加工成成熟的tRNA。基于这些观察结果，加州贻贝和紫贻贝的四臂tRNASer(UCN)序列被解释为假tRNASer(UCN)基因。
