青霉素G酰化酶调节基因的定位

Localization of Regulatory Gene in Penicillin G Acylase Operon

为了定位青霉素Ｇ酰化酶的调节基因，从质粒ｐＰＡ６克隆了一系列青霉素Ｇ酰化酶基因（ｐａｃ）的片段，将这些重组质粒转化Ｅ．ｃｏｌｉＤ８１６，测定克隆片段对ｐａｃ表达的影响。如果克隆片段含有完整的调节基因（ｐａｃＲ），诱导剂不能使由高拷贝ｐａｃＲ表达的阻抑物失活，部分阻抑物结合ｐａｃ操纵基因，阻碍ＲＮＡ聚合酶对ｐａｃ的转录，因此ｐａｃ的表达量降低。发酵结果表明，阻抑物可能是由ｐａｃ结构基因内部的ＯＲＦⅡ编码的蛋白因子。

A set of segments from pPA6 which contained pac gene were subcloned to plasmid pOK12 or pBR322,and the recombinant plasmids were transformed into E.coli D816 containing an intact pac operon on it′s chromosome,then the effects of cloned segments on pac expression were estimated.If the cloned DNA fragment contained pac regulatory gene(pacR),then inducers could not bind and inactivate all the repressors encoded by high copy number plasmid harbouring pac R,Additionally some active repressors bound pac operator on chromosome and obstructed RNA polymerase from transcripting the pac,then the expression of pac decreased;The results indicated that the pac R is within the (Taq IDra I)fragment about 500bp in size within the pac structure gene and ORFⅠ and ORFⅡ were the canditates for pac R.