Xu Delin, Kwon Hyung-Jin, Suh Joo-Won
Department of Biological Science, Institute of Bioscience and Biotechnology, Myongji University, San 38-2 Namdong, Yongin, 449-728, South Korea.
Arch Microbiol. 2008 Apr;189(4):419-26. doi: 10.1007/s00203-007-0336-4. Epub 2007 Dec 14.
In the present study, a mechanism for S-adenosylmethionine (SAM) to promote secondary metabolism was characterized in terms of bldH sl) expression in Streptomyces lividans. A previous study demonstrated that SAM, on application at 2 microM, induces the transcription of the strR promoter (strRp), which originates from Streptomyces griseus, in S. lividans. An inactivation study verified that bldH sl is essential to strRp transcription in S. lividans and it was demonstrated that the effects of SAM on the induction of strRp activity, on the transcription of redZ and actII-orf4, and on antibiotic production were compromised when the unique leucine TTA-codon of bldH sl was changed to TTG. Western blot analysis revealed that SAM supplementation enhances the expression of bldH sl when the TTA-codon was intact but not when the TTG replacement was provided. This study validates the involvement of BldH sl in the potentiating effect of SAM on the antibiotic production and substantiates that SAM controls the expression of bldH sl through the TTA-codon control in translating bldH mRNA. It is argued here that the intracellular SAM-level modulates the maturation of bldA, which encodes the UUA-codon tRNA and controls secondary metabolism in S. lividans.
在本研究中，根据变铅青链霉菌中bldH sl)的表达情况，对S-腺苷甲硫氨酸（SAM）促进次级代谢的机制进行了表征。先前的一项研究表明，在变铅青链霉菌中，以2 microM的浓度施用SAM可诱导源自灰色链霉菌的strR启动子（strRp）的转录。一项失活研究证实，bldH sl对变铅青链霉菌中strRp的转录至关重要，并且当bldH sl独特的亮氨酸TTA密码子变为TTG时，SAM对strRp活性诱导、redZ和actII-orf4转录以及抗生素产生的影响均受到损害。蛋白质印迹分析表明，当TTA密码子完整时，补充SAM可增强bldH sl的表达，但当提供TTG替代时则不然。本研究证实了BldH sl参与了SAM对抗生素产生的增强作用，并证实SAM通过在翻译bldH mRNA时控制TTA密码子来控制bldH sl的表达。本文认为，细胞内SAM水平调节bldA的成熟，bldA编码UUA密码子tRNA并控制变铅青链霉菌中的次级代谢。
