Fluorescent RNA is an important analytical tool in medical diagnostics, RNA cytochemistry, and RNA aptamer development. We have synthesized the fluorescent ribonucleotide analogue 1,3-diaza-2-oxophenothiazine-ribose-5′-triphosphate (tCTP) and tested it as substrate for T7 RNA polymerase in transcription reactions, a convenient route for generating RNA in vitro. When transcribing a guanine, T7 RNA polymerase incorporates tCTP with 2-fold higher catalytic efficiency than CTP and efficiently polymerizes additional NTPs onto the tC. Remarkably, T7 RNA polymerase does not incorporate tCTP with the same ambivalence opposite guanine and adenine with which DNA polymerases incorporate the analogous dtCTP. While several DNA polymerases discriminated against a d(tC-A) base pair only by factors <10, T7 RNA polymerase discriminates against tC-A base pair formation by factors of 40 and 300 when operating in the elongation and initiation mode, respectively. These catalytic properties make T7 RNA polymerase an ideal tool for synthesizing large fluorescent RNA, as we demonstrated by generating a ∼800 nucleotide RNA in which every cytosine was replaced with tC.
荧光 RNA 是医学诊断、RNA 细胞
化学和 RNA 适体开发中的重要分析工具。我们合成了荧光
核糖核苷酸类似物 1,3-二氮杂-2-氧
吩噻嗪-
核糖-5'-
三磷酸 (tCTP),并在转录反应中测试其作为 T7 RNA 聚合酶的底物,这是体外生成 RNA 的便捷途径。当转录
鸟嘌呤时,T7 RNA 聚合酶以比 CTP 高 2 倍的催化效率掺入 tCTP,并有效地将额外的 NTP 聚合到 tC 上。值得注意的是,T7 RNA 聚合酶不会掺入具有与
鸟嘌呤和
腺嘌呤相反的相同矛盾的 tCTP,而
DNA 聚合酶则掺入类似的 dtCTP。虽然一些
DNA 聚合酶仅以 <10 倍的因子来区分 d(tC-A) 碱基对,但当在延伸和起始模式下操作时,T7 RNA 聚合酶分别以 40 和 300 的因子来区分 tC-A 碱基对的形成。这些催化特性使 T7 RNA 聚合酶成为合成大荧光 RNA 的理想工具,正如我们通过生成约 800 个核苷酸的 RNA(其中每个
胞嘧啶都被 tC 取代)所证明的那样。