Comparative genomic analysis reveals a novel mitochondrial isoform of human rTS protein and unusual phylogenetic distribution of the rTS gene.
Comparative genomic analysis reveals a novel mitochondrial isoform of human rTS protein and unusual phylogenetic distribution of the rTS gene.
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DOI：
10.1186/1471-2164-6-125
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发表时间：
2005-09-14
期刊：
影响因子：
4.4
通讯作者：
Dolnick, Bruce J
中科院分区：
文献类型：
--
作者：
Liang, Ping;Nair, Jayakumar R;Song, Lei;McGuire, John J;Dolnick, Bruce J
rTS基因（ENOSF1）最初在智人中被鉴定为与胸苷酸合成酶（TYMS）mRNA互补的基因，已知其编码两种蛋白质异构体，rTSα和rTSβ。rTSβ异构体似乎是一种负责合成参与胸苷酸合成酶下调的信号分子的酶，但rTS基因的确切细胞功能在很大程度上是未知的。
通过比较基因组序列分析，我们预测存在一种新的蛋白质异构体rTS，由于利用了位于rTSβ起始密码子上游的一个替代起始密码子，它的N端比rTSβ长27个残基。我们观察到，在所有有基因组序列的rTS基因中都可以预测到类似的延长的N端，并且从细菌到人类，这些延长区域是保守的。因此，我们推断具有延长N端的蛋白质可能代表rTS蛋白质的一种祖先形式。序列分析强烈预测人rTSγ延长的N端存在一个线粒体信号序列，而rTSβ中没有。我们通过证明亚细胞分级分离得到的线粒体中存在rTSγ和rTSβ两种蛋白质，从实验上证实了人线粒体中rTS的存在。此外，我们对rTS直系同源序列的综合分析揭示了该基因不寻常的系统发育分布，这表明发生了一次或多次水平基因转移事件。
线粒体中存在两种rTS异构体表明rTS信号通路可能在线粒体内部是活跃的。我们的报告还提供了一个通过比较基因组分析鉴定新的蛋白质异构体以及改进基因注释的实例。
The rTS gene (ENOSF1), first identified in Homo sapiens as a gene complementary to the thymidylate synthase (TYMS) mRNA, is known to encode two protein isoforms, rTSα and rTSβ. The rTSβ isoform appears to be an enzyme responsible for the synthesis of signaling molecules involved in the down-regulation of thymidylate synthase, but the exact cellular functions of rTS genes are largely unknown. Through comparative genomic sequence analysis, we predicted the existence of a novel protein isoform, rTS, which has a 27 residue longer N-terminus by virtue of utilizing an alternative start codon located upstream of the start codon in rTSβ. We observed that a similar extended N-terminus could be predicted in all rTS genes for which genomic sequences are available and the extended regions are conserved from bacteria to human. Therefore, we reasoned that the protein with the extended N-terminus might represent an ancestral form of the rTS protein. Sequence analysis strongly predicts a mitochondrial signal sequence in the extended N-terminal of human rTSγ, which is absent in rTSβ. We confirmed the existence of rTS in human mitochondria experimentally by demonstrating the presence of both rTSγ and rTSβ proteins in mitochondria isolated by subcellular fractionation. In addition, our comprehensive analysis of rTS orthologous sequences reveals an unusual phylogenetic distribution of this gene, which suggests the occurrence of one or more horizontal gene transfer events. The presence of two rTS isoforms in mitochondria suggests that the rTS signaling pathway may be active within mitochondria. Our report also presents an example of identifying novel protein isoforms and for improving gene annotation through comparative genomic analysis.