E．coli核糖体蛋白质S12依赖链霉素突变抑制λN基因表达的分子机制

Molecular Mechanism of Suppressing λN Gene's Expression in E.coli Ribosomal Protein S12 Streptomycin-dependent Mutant

本文利用ＰＣＲ方法克隆了Ｅ．ｃｏｌｉＴ８３依赖链霉素（ｓｔｅｒｐｔｏｍｙｅｉｎｄｅｐｅｎｄｅｎｔ，Ｓｍ＾ｄ）菌株中编码突变的核糖体蛋白质Ｓ１２的ｒｐｓＬ＾ｄ基因，并进行了ＤＮＡ序列分析，发现第４２位密码子由编码赖氨酸（Ｌｙｓ，Ｋ）的ＡＡＡ变为编码谷氨酰胺（Ｇｌｎ，Ｑ）的ＣＡＡ。依据Ｇａｒｎｉｅｒ原理预测了突变对Ｓ１２蛋白质二级结构形成趋势的影响，结果表明。

Using the polymerase chain reaction(PCR)method, the rpsL￣d gene was amplified and cloned,which encodes the streptomycin-dependent(Sm￣d)mutant of ribosomal protein S12 in E.coli T83.The result of DNA sequencing showed an AAA to CAA mutation at codon 42,leading to the substitution of glutamine(Gln,Q)for lysine(Lys,K).According to the principle of Garnier,we predicted that there might be alterations in the secondary structural propensity of protein S12 due to the mutation. The outcome indicated that the β-turn propensity at position 42 and its nearby region was increased evidently and the relative position of relevant subdomains were changed. As a result,the special conformation of the whole protein S12 was influenced.In view of that ribosomal proteins and ribosomal RNAs(rRNA)mutually adapted in structures and functions,the probable molecular mechanism.That how protein S12 Smdmutant in E.coli T83 suppressed λN gene's expression is discussed.