ENZYMATIC RECOGNITION OF THE BASE-PAIR BETWEEN ISOCYTIDINE AND ISOGUANOSINE
ENZYMATIC RECOGNITION OF THE BASE-PAIR BETWEEN ISOCYTIDINE AND ISOGUANOSINE
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DOI：
10.1021/bi00090a027
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发表时间：
1993-10-05
期刊：
影响因子：
2.9
通讯作者：
BENNER, SA
中科院分区：
文献类型：
--
作者：
SWITZER, CY;MORONEY, SE;BENNER, SA
研究了不同聚合酶催化双链寡核苷酸中异鸟嘌呤(iso-G)和异胞嘧啶(iso-C)之间的模板导向碱基对形成的能力。开发了一种利用自动DNA合成仪制备适合于掺入DNA的脱氧异鸟苷衍生物的新方法。T7RNA聚合酶、AMV逆转录酶和DNA聚合酶的Klenow片段都将iso-G与iso-C相反地掺入到模板中。T4DNA聚合酶则无此作用。几种聚合酶也加入了与T相反的iso-G，可能是通过与与T互补的次要互变形式的iso-G配对。在模板中，当Klenow片段为催化剂时，iso-G引导iso-C和T的掺入，而当T7RNA聚合酶为催化剂时，iso-G仅指导U的掺入。此外，在自动合成寡核苷酸后，发现iso-C的衍生物在碱性条件下经历了大量的脱胺反应，用于碱基脱保护。Iso-C的脱氨基反应和iso-G的相互矛盾的互变异构形式都使得(iso-C).(ISO-G)碱基对不太可能是信息存储分子的一部分，也包含在地球上数十亿年前出现的原始生命形式中发现的A.T和G.C碱基对。然而，基因字母表中的额外字母在当代实验室环境中可以发挥有用的作用。
The ability of various polymerases to catalyze the template-directed formation of a base pair between isoguanine (iso-G) and isocytosine (iso-C) in duplex oligonucleotides has been investigated. A new procedure was developed for preparing derivatives of deoxyisoguanosine suitable for incorporation into DNA using an automated DNA synthesizer. T7 RNA polymerase, AMV reverse transcriptase, and the Klenow fragment of DNA polymerase all incorporated iso-G opposite iso-C in a template. T4 DNA polymerase did not. Several polymerases also incorporated iso-G opposite T, presumably through pairing with a minor tautomeric form of iso-G complementary to T. In a template, iso-G directs the incorporation of both iso-C and T when Klenow fragment is the catalyst and only U when T7 RNA polymerase is the catalyst. Further, derivatives of iso-C were found to undergo significant amounts of deamination under alkaline conditions used for base deprotection after automated oligonucleotide synthesis. Both the deamination reaction of iso-C and the ambivalent tautomeric forms of iso-G make it unlikely that the (iso-C).(iso-G) base pair was a part of information storage molecules also containing the A.T and G.C base pairs found in primitive forms of life that emerged on planet earth several billion years ago. Nevertheless, the extra letters in the genetic alphabet can serve useful roles in a contemporary laboratory setting.