LIM class homeobox gene is one of the key gene s controlling embryonic development of animal. In order to clone the entire sequ ence of amphioxus LIM class homeobox gene, adult amphioxus was acquired in Shazi k ou sea field in Qingdao City in June 1997, and the amplification methodology of Amphioxus (Branchiostoma belcheri tsingtauense) LIM class homeobox gene frag ment by PCR was studied. The amplification by means of single pair of primers an d single PCR operation failed to produce specific PCR product, and amplification by means of single pair of primers and twice PCR operations failed, too. In the study of nested-PCR, amplification by means of general PCR approach was not sat isfactory, but amplifications by means of three steps-two stages approach and by four steps-two stages method were successful. The sequencing data of PCR produc t acquired by these two methods show a high accordance with genomic DNA sequenci n g data of this gene fragment. Therefore, the PCR products, amplified by these tw o methods, were extremely specific. In comparison with the PCR approaches mentio ned, nested-PCR by means of the three-step and two-stage approach and by means o f the four-step and two-stage approach were the best to amplify unidentified gen e fragments with degenerated primers.%于1997年6月在青岛市沙子口海域采集文昌鱼样品，采用RT-PCR方法进行青岛文昌鱼LIM类同源框基因片段的扩增研究。结果表明，用一对 引物一次PCR扩增的方法未能得到特异的PCR产物，用一对引物两次PCR扩增的方法也同样未 果。在对套式PCR进行研究时发现，用普遍PCR方法进行的套式PCR结果不够理想，而用三步 两段法和四步两段法套式PCR则可进行成功的扩增。用这两种方法扩增的PCR产物具有高度特 异 性。相比之下，用简并的引物对未知的基因片段进行PCR扩增时，三步两段法和四步两段法 的套式PCR应是首选方法。
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