DNA Unwinding Assay Kit
This kit is designed to investigate whether a compound intercalates into the DNA double-helix, or binds in the groove, leading to unwinding of the DNA. This is a characteristic of a number of inhibitors of DNA-modifying enzymes such as the topoisomerase inhibitor m-amsacrine.
Intercalators contain planar, normally polycyclic, aromatic structures which can insert between the bases of the double-helical DNA molecule. Compounds which are able to intercalate into DNA or bind in the groove can lead to local unwinding of the DNA leading to a decrease in the twist of the DNA. If a DNA molecule is nicked and rejoined (for example by a topoisomerase) in the presence of such a compound, then the result is relaxed, underwound DNA; on removal of the enzyme and compound this converts to supercoiled DNA. The supercoiled DNA formed in these conditions is indicative of an intercalator.
This is the basis of the DNA unwinding assay. Supercoiled (or relaxed) plasmid DNA is incubated briefly with the test compound prior to relaxation by the wheat germ topo I. The enzyme and drug are then removed by extraction and the plasmid analysed by gel electrophoresis. Supercoiled topoiosmers indicate the compound is an intercalator or groove binder. If the compound is not an intercalator then the product will be relaxed plasmid.
The assay should be checked by performing a control reaction using relaxed plasmid to show that the compound is not simply acting as an inhibitor of the topo I.
The kit (product code DUKSR001) contains all you need to do the assay including:-
Supercoiled pBR322 (50 μg), relaxed pBR322 (25 μg), wheat germ topo I (250 U), Assay Buffer (1 ml) and Dilution Buffer (1 ml).
We also supply kits which contain topo I and buffers but only:-
(i) the relaxed form of pBR322 (product code DUKR002). This will show if a compound is an intercalator but not if it also inhibits the topo I (i.e. false-negatives are possible)
(ii) the supercoiled form of pBR322 (product code DUKS003). This will show if a compound is an intercalator but the same result will be given if it is an inhibitor of topo I (i.e. false-positives are possible)
This is illustrated in the scheme below:
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我在做5RACE,选用TaKaRa公司的RNA反转录酶（RNaseH-），不知道这个酶好不好，有什么需要注意的。
没有序列识别的功能，他就是简单的催化相邻DNA链的5-P末端和3'-OH末端以磷酸二酯键结合的反应，需ATP作辅酶。 不仅可以催化粘性末端之间或平滑末端之间的DNA的连接，也催化DNA与RNA之间以及少数RNA之间的连接。
反转录酶（Reversetranscripatase）是以RNA为模板指导三磷酸脱氧核苷酸合成互补DNA（cDNA）的酶。哺乳类C型病毒的反转录酶和鼠类B型病毒的反转录酶都是一条多肽链。鸟类RNA病毒的反转录酶则由两上亚基结构。真核生物中也都分离出具有不同结构的反转录酶。
