Lehmann K A, Bass B L
Department of Biochemistry and HHMI, University of Utah, 50 North Medical Drive, Room 211, Salt Lake City, Utah 84132, USA.
Biochemistry. 2000 Oct 24;39(42):12875-84. doi: 10.1021/bi001383g.
Adenosine deaminases that act on RNA (ADARs) deaminate adenosines to produce inosines within RNAs that are largely double-stranded (ds). Like most dsRNA binding proteins, the enzymes will bind to any dsRNA without apparent sequence specificity. However, once bound, ADARs deaminate certain adenosines more efficiently than others. Most of what is known about the intrinsic deamination specificity of ADARs derives from analyses of Xenopus ADAR1. In addition to ADAR1, mammalian cells have a second ADAR, named ADAR2; the deamination specificity of this enzyme has not been rigorously studied. Here we directly compare the specificity of human ADAR1 and ADAR2. We find that, like ADAR1, ADAR2 has a 5' neighbor preference (A approximately U > C = G), but, unlike ADAR1, also has a 3' neighbor preference (U = G > C = A). Simultaneous analysis of both neighbor preferences reveals that ADAR2 prefers certain trinucleotide sequences (UAU, AAG, UAG, AAU). In addition to characterizing ADAR2 preferences, we analyzed the fraction of adenosines deaminated in a given RNA at complete reaction, or the enzyme's selectivity. We find that ADAR1 and ADAR2 deaminate a given RNA with the same selectivity, and this appears to be dictated by features of the RNA substrate. Finally, we observed that Xenopus and human ADAR1 deaminate the same adenosines on all RNAs tested, emphasizing the similarity of ADAR1 in these two species. Our data add substantially to the understanding of ADAR2 specificity, and aid in efforts to predict which ADAR deaminates a given editing site adenosine in vivo.
作用于RNA的腺苷脱氨酶（ADARs）将腺苷脱氨，在很大程度上为双链（ds）的RNA中产生肌苷。与大多数双链RNA结合蛋白一样，这些酶会结合任何双链RNA，且无明显的序列特异性。然而，一旦结合，ADARs对某些腺苷的脱氨效率会高于其他腺苷。目前已知的关于ADARs内在脱氨特异性的大部分信息都来自于对非洲爪蟾ADAR1的分析。除了ADAR1，哺乳动物细胞还有第二种ADAR，名为ADAR2；该酶的脱氨特异性尚未得到严格研究。在此，我们直接比较了人类ADAR1和ADAR2的特异性。我们发现，与ADAR1一样，ADAR2具有5'邻位偏好（A约>U>C = G），但与ADAR1不同的是，它也有3'邻位偏好（U = G>C = A）。对这两种邻位偏好的同时分析表明，ADAR2偏好某些三核苷酸序列（UAU、AAG、UAG、AAU）。除了表征ADAR2的偏好外，我们还分析了在完全反应时给定RNA中被脱氨的腺苷比例，即该酶的选择性。我们发现ADAR1和ADAR2以相同的选择性使给定的RNA脱氨，这似乎由RNA底物的特征所决定。最后，我们观察到非洲爪蟾和人类ADAR1在所有测试的RNA上使相同的腺苷脱氨，强调了这两个物种中ADAR1的相似性。我们的数据极大地增进了对ADAR2特异性的理解，并有助于预测在体内哪个ADAR会使给定编辑位点的腺苷脱氨。
