摘要
rnc,era基因是大肠杆菌两个相邻的基因。用S_1核酸酶图谱法测得转录从rnc基因伸延到era基因。当rnc基因突变使所产生的RNaseⅢ丧失活性时,大肠杆菌中RNaseⅢ和Era蛋白的合成速度同对上升,且上升幅度相同,合成量相等。将此二基因分别或一起克隆入质粒并置于P_L起动子下游时,rnc能表达产生RNaseⅢ;rnc-era能表达产生RNaseⅢ和Era两种蛋白质,单独era则虽能转录却不产生Era蛋白。实验证明:era基因的表达依赖于rnc基因的表达,在体内两者共表达体现在转录和翻译水平上,两个基因同属于一个操纵子,共同受RNaseⅢ活性的反馈调节。单独转录的era-mRNA因缺乏有效的翻译起始序列而不能被翻译。
rnc and era are two contigous genes in E. coli. Extending of the transcription from rnc to era has been proved by means of S1 nuclease mapping. Both RNaseⅢ and Era protein has the same synthetic amount and both synthetic rate rose up to the same extent in rnc mutant resulting in RNaseⅢ inativation. Subcloning these genes into a plasmid under the control of PL promoter, rnc gene overexpressed RNaseⅢ) rnc-era overexpressed both RNaseⅢ and Era protien; era gene alone, however, could not produce Era protein. The results show that the expression of era depends 6n that of rnc gene. These two genes are of coexpression both in transcriptional and translational level in vivo and belong to the same rnc operon which expression is feed-backly controled by RNaseⅢactivity. era-mRNA alone could not be translated due to lacking of efficient translational initiation sequences.