耐热链霉菌4″-O-异戊酰基转移酶基因在变铅青链霉菌TK24中的表达

Expression of 4″-O-isovaleryltransferase gene from Streptomyces thermotolerans in Streptomyces lividans TK24

拟研究异源调控系统提高耐热链霉菌Streptomyces thermotolerans 4″-O-异戊酰基转移酶基因（ist）表达的可能性。在麦迪霉素产生菌Streptomyces mycarofaciens 1748中曾克隆到BamHⅠ~8.0 kb片段,含此基因片段的变铅青链霉菌TK24 Streptomyces lividans TK24转化子可将螺旋霉素高效转化为丙酰螺旋霉素。序列分析表明此片段除包含麦迪霉素4″-O-丙酰基转移酶基因（mpt）外还存在与其连锁的两个正调控基因orf27和orf28。将这个基因簇中mpt基因的orf替换为ist基因的orf,然后与两个正调控基因或者单独一个orf27连接,将这些构建好的片段分别克隆到中等拷贝数及高拷贝数载体pKC1139和pWHM3上,再转化到S.lividans TK24中。通过测定S.lividans TK24转化子中螺旋霉素生物转化为4″-O-酰化螺旋霉素的产率来评价mpt和ist基因的表达水平。结果表明只有高拷贝载体pWHM3构建的重组质粒S.lividans TK24转化子中才能明显检测到4″-O-异戊酰螺旋霉素的产生。mpt基因的正调节系统可以提高ist基因的表达水平,含两个调节基因的转化子转化效率高于含单一调节基因的转化子。

4＂-O-isovaleryltransferase gene （ist） was regulated by positive regulatory genes of midecamycin 4＂-O-propionyltransferase gene （mpt） in Streptomyces lividans TK24. A BamH I-8.0 kb fragment from Streptomyces mycarofaciens 1748 was proved that it contained mpt gene and linked with two positive regulatory genes, orf27 and orf28. Orf of mpt was replaced by orf of ist and linked with two regulatory genes or orf27 single, and individually cloned into the vectors pKC1139 or pWHM3 （high copy number）, and then transformed into S. lividans TK24. The levels of mpt and ist expression were evaluated by the bio-tramsformation efficacy of spiramycin into 4＂-O-acylspiramycins in these transformants. The results showed that 4＂-O-isovalerylspiramycins could be detected only in the transformants containing the plasmids constructed with pWHM3. The efficacy of bio-transformation of the transformants containing two regulatory genes was higher than that of off27 single. So, the positive regulatory genes system ofmpt gene could enhance ist gene expression.