聚合酶链反应用于高效的基因改造

本文报道利用近年来发展起来的基因体外扩增技术——聚合酶链反应(PCR)进行高效的基因定向改造的结果。在构建新的EcoRI基因表达质粒时,为了在EcoRⅠ基因SD序列前改变一个碱基引入SalⅠ切点以缺失其启动子,同时将Glul44改造成Lys,我们回收分离pER101的1.5kb SalⅠ/PatⅠ片段作为模板,合成各带一个错配的两个25聚DNA片段作为扩增引物,利用Taq DNA聚合酶进行PCR扩增,结果经过30个循环,从约0.05μg模板DNA得到约10μg的0.49kbDNA。根据理论计算,扩增产物中突变片段占99％以上。用SalⅠ/BglⅠ酶切克隆入pUCl9 SalⅡ/BamHI,任意取两个重组子进行序列分析结果表明都发生了预期的突变。扩增产物已被克隆入pER304,使得EcoRl(Lys-144)基因置于PL下游以实现其控制的高表达。     

EcoRI N端肽段的定点缺失研究

本文报道了一种定点缺失任意大小的DNA片段的基因裁剪方法,它建立于聚合酶链反应(PCR)的扩增、Klenow平端修饰和克隆等过程.所建立的方法被用来研究了EcoRI,方便地构建了两个从N端开始的缺失突变株EcoRI(Δ45aa)和EcoRI(Δ89aa),这说明所建立的定点缺失方法是有效的;突变株的SDS-PAGE和底物结合试验等结果表明:螺旋(29—43)对于EcoRI结合底物GAATTC十分重要.     

SITE-SPECIFIC DELETION OF THE N-TERMINAL SEGMENTS FROM EcoRI ENDONUCLEASE USING THE POLYMERASE CHAIN REACTION

We developed a general and efficient method for directing the deletions of DNA sequences of any lengths using polymerase chain reaction (PCR). The method was based on in vitro amplification of target sequences with site-specific deletions, Klenow end-flushing and blunt-end cloning. As an example, it was used to delete the restriction gene encoding EcoRI endonuclease, resulting in plasmids expressing two truncated forms. Assays using SDS-PAGE and gel retardation revealed the important role of the amphipathic helix (29-43) of the EcoRI endonuclease in binding to its cognate substrate.     

AN EFFICIENT SITE-DIRECTED MUTAGENESIS USING POLYMERASE CHAIN REACTION

We report here a simple and efficient method for site-directed mutagenesis using polymer-ase chain reaction (PCR). In constructing a new expression plasmid for the EcoRI restrictiongene, we made two point mutations. While one created a new Sall site prior to the SDsequence, the other replaced Glu144 with Lys. A 1.5 kb Sall-PstI fragment isolated frompER101 was used as the template. Two 25 mer oligonucleotide primers containing the de-sired mutations were synthesized and used to direct PCR amplification with Taq DNA poly-merase. About 0.5μg of the 0.49 kb fragment was obtained from 0.05 μ of the 1.5 kb frag-ment by carrying out polymerase chain reaction for 30 cycles. As calculated theoretically,99% of the product contained the desired mutations. The product was cloned into pUC19using Sall and PstI, two of the transformed colonies were randomly chosen for sequence anal-ysis, and both of them were shown to contain the desired mutations. Finally, the amplifiedfragment was cloned into pER304 to place the