大肠杆菌离子束诱变及rpoB基因两个新的利福平抗性位点鉴定

以60Co-γ射线辐照为参照体系，研究了低能氮离子诱发大肠杆菌利福平抗性突变。结果表明，低能氮离子注入具有损伤轻而突变率较高的特点。碱基置换型突变与其检出频率分析表明，CG→TA、GC→AT、AT→GC转换与AT→TA颠换为低能氮离子诱发大肠杆菌活体细胞内的高频突变，占检出总突变数的875% (77/88)。并鉴定出大肠杆菌rpoB基因中两个新的利福平抗性决定位点。位点一位于1551位鸟嘌呤脱氧核苷酸（dG）被胞嘧啶脱氧核苷酸（dC）取代，导致Gln517 (谷氨酰胺残基) 被His (组氨酸) 替代；位点二位于1692的胞嘧啶脱氧核苷酸（dC）被胸腺嘧啶脱氧核苷酸（dT）替代，导致Pro564 (脯氨酸残基) 被Leu (亮氨酸) 取代，使突变子产生抗性。其中位点一还未见报道，位点二的同义突变已有报道，但1692位点C到T的核苷酸突变并没有得到鉴定。

Mutagenesis of Ion Beam Implantation and Identification of Two New Rifampicin Resistance Determining Sites in rpoB Gene in Escherichia coli

The rifampicin resistance mutations induced by low energy nitrogen ion implantation had been investigated in this study referred to the study of 60Co-gamma ray irradiation. It is suggested that low energy nitrogen ion beam implantation might generate a lower damage but get higher mutation rates than 60Co-gamma ray irradiation did. The frequencies showed the preference of base substitutions induced by N+ ion beam are CG--> TA transition, GC-->AT transition, AT--> GC transition and AT-->TA transversion which occupy 87.5% (77/88) of the total mutation of base substitutions. Two new rif-determining sites had also been identified in rpoB gene in Escherichia coli. The first new site located in 1551. When dG1551 was replaced by dC, it resulted in Gln517 was substituted by a histidine. The other new site located in 1692. When dC1692 was replaced by dT, it resulted in a Pro564 is changed into a leucine. The synonymous mutation of the second site had been reported but the nucleotide substitution, dC-->dT, had not been identified before.