代谢
链霉菌属弗拉德菌的泰乐菌素生物合成(tyl)基因簇包含辅助基因,这些基因编码通常与初级代谢相关的功能。这些基因的破坏不会导致生存能力的丧失,因为基因组其他位置也存在着等效基因(可能用于“看家”目的)。tyl簇还包含两个编码与数据库中任何蛋白质都不同的产物的基因。两个辅助基因,metF(编码N5,N10-亚甲基四氢叶酸还原酶)和metK(编码S-腺苷甲硫氨酸合成酶),位于tyl簇中的一个“未知”基因(orf9)的两侧。在所有这三个基因都被破坏的弗拉德菌菌株中,泰乐菌素的产量降低了,尽管这种效果在补充了甘氨酸甜菜碱的培养基中被掩盖了,因为甘氨酸甜菜碱可以向四氢叶酸池提供甲基。显然,将辅助基因招募到tyl簇的一个后果是增强了次级代谢期间转甲基的能力。
The tylosin-biosynthetic (tyl) gene cluster of Streptomyces fradiae contains ancillary genes that encode functions normally associated with primary metabolism. These can be disrupted without loss of viability, since equivalent genes (presumably used for 'housekeeping' purposes) are also present elsewhere in the genome. The tyl cluster also contains two genes that encode products unlike any proteins in the databases. Two ancillary genes, metF (encoding N5,N10-methylenetetrahydrofolate reductase) and metK, encoding S-adenosylmethionine synthase, flank one of the 'unknown' genes (orf9) in the tyl cluster. In a strain of S. fradiae in which all three of these genes were disrupted, tylosin production was reduced, although this effect was obscured in media supplemented with glycine betaine which can donate methyl groups to the tetrahydrofolate pool. Apparently, one consequence of the recruitment of ancillary genes into the tyl cluster is enhanced capacity for transmethylation during secondary metabolism.
来源:Hazardous Substances Data Bank (HSDB)