Chambers J C, Kenan D, Martin B J, Keene J D
Department of Microbiology and Immunology, Duke University Medical Center, Durham, North Carolina 27710.
J Biol Chem. 1988 Dec 5;263(34):18043-51.
La is an autoimmune RNA-binding protein of 47 kDa that plays a role in the transcription of RNA polymerase III. Both genomic and complementary DNAs were isolated that encompass the coding sequence of the human La molecule. The genomic clones encompass 11 exons and a putative G/C-rich promoter upstream of the mRNA start site. The cDNA sequence encodes a protein of 408 amino acids and can be divided into two structural domains based upon amino acid content and protease sensitivity. An unusually long stretch of 130 amino acids, much of which was predicted to form a stable alpha-helix, was found near the middle of the protein between the two domains. A ribonucleoprotein (RNP) consensus sequence was found just NH2-terminal to the long alpha-helix. The RNP consensus sequence is split into two exons by the fifth intron. Expression of three separate fragments of the La protein in Escherichia coli showed that a strongly autoimmune-reactive portion resides in the fragment containing the RNP consensus sequence and most of the long alpha-helical core. Autoantibodies from La patients also reacted with the terminal regions of the protein, but the extent of reactivity varied among patients. Differences in reactivity of autoantibodies to each portion of La protein may reflect an evolution of recognition of different epitopes during the development of the autoimmune response. These findings support an antigen-driven mechanism for autoimmune reactivity.
La是一种47 kDa的自身免疫性RNA结合蛋白，在RNA聚合酶III的转录中发挥作用。已分离出包含人类La分子编码序列的基因组DNA和互补DNA。基因组克隆包含11个外显子以及mRNA起始位点上游一个假定的富含G/C的启动子。cDNA序列编码一个408个氨基酸的蛋白质，根据氨基酸含量和蛋白酶敏感性可分为两个结构域。在该蛋白质两个结构域之间的中部附近发现了一段异常长的130个氨基酸序列，其中大部分预计会形成一个稳定的α螺旋。在长α螺旋的NH2端紧邻处发现了一个核糖核蛋白（RNP）共有序列。RNP共有序列被第五个内含子分成两个外显子。在大肠杆菌中表达La蛋白的三个单独片段表明，一个强自身免疫反应性部分位于包含RNP共有序列和大部分长α螺旋核心的片段中。来自La患者的自身抗体也与该蛋白的末端区域发生反应，但不同患者之间的反应程度有所不同。自身抗体对La蛋白各部分反应性的差异可能反映了自身免疫反应发展过程中对不同表位识别的演变。这些发现支持了自身免疫反应性的抗原驱动机制。
