Threonine operon의 leader sequence의 mRNA 2차 구조가 threonine operon의 발현에 미치는 영향 = Effect of secondary structure of mRNA in the leader sequence on the expression of threonine operon

국문 초록 (Abstract)

L-threonine 은 필수아미노산 중 하나이며 분자량은 119.12이고 무취의 백색 결정 분말로 단맛을 지닌다. 또한 E. coli의 threonine operon은 thrA, thrB, thrC인 3개의 structural gene 과 thrA 앞에 regulatory region이 존재한다. 각각의 structural gene은aspartokinase I-homoserine dehydrogenase I, homoserine kinase, threonine synthase를 coding 한다. E. coli내에서 threonine 합성에 관여하는 효소의 발현은 transcriptional attenuation에 의해 조절 받는다. Threonine 합성에 관여하는 효소들의 발현을 조절하는 attenuator regio을 일부 제거하고, 이로 인해 형성되는 attenuator region의 mRNA의 2차구조가 변화함으로서 threonine 생성량에 어떤 영향을 미치는가를 알아보았다. 그 결과 attenuator 의 secondary structure형성이 파괴되어 threonine 생성량이 증가되거나 감소된 mutnt들을 얻었다. 이는 leader sequence의 attenuator에 있는 terminator의 2차구조가 변형되면서 threonine operon이 constituticve expression 되거나, 낮은 수준으로 발현되기 때문인 것이로 밝혀졌다.

다국어 초록 (Multilingual Abstract)

L-threonine is an essential amino acid which has the MW of 119.12. E coli thr operon consists of thrA, thrB and thrC and a regulatory region. Each structural gene codes for the aspartokinase I -homoscrine dehydrogenase I, homoserine kinase, and threonine synthase, respectively. The biosynthesis of threonine is regulated by the repression with threonine and isoleucine and the the expression of the gene is also regulated by attenuation. The effect of secondry structure of mRNA in the leader sequence on the expression of threonine operon was studied by deletion of the attenuator with Ba131. The plasmids which caused the increase or decrease in the productivity of threonine in E. coli were obtained. The changes in the productivity were due to the destruction of secondary structure of mRNA around the attenuator in the leader sequence. Among them, plasmid pE2, pA4 and pA11 showed constitutive expression of thr operon by the disruption of transcription terminator. Another plasmid pE1 and pE16 showed decrease in the productivity by the too much deletion of the leader sequence. These results indicated that the change in the secondary structure of mRNA in the leader sequence in thr operon affected the productivity of threonine in E. coli.