State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China.
Department of Applied Biology, East China University of Science and Technology, Shanghai, China.
Appl Microbiol Biotechnol. 2018 May;102(9):4101-4115. doi: 10.1007/s00253-018-8900-1. Epub 2018 Mar 17.
Global regulator BldA, the only tRNA for a rare leucine codon UUA, is best known for its ability to affect morphological differentiation and secondary metabolism in the genus Streptomyces. In this study, we confirmed the regulatory function of the bldA gene (Genbank accession no. EU124663.1) in Streptomyces lincolnensis. Disruption of bldA hinders the sporulation and lincomycin production, that can recur when complemented with a functional bldA gene. Western blotting assays demonstrate that translation of the lmbB2 gene which encodes a L-tyrosine hydroxylase is absolutely dependent on BldA; however, mistranslation of the lmbU gene which encodes a cluster-situated regulator (CSR) is observed in a bldA mutant. Intriguingly, when the preferential cognate codon CTG was used, the expression level of LmbU was not the highest compared to the usage of rare codon TTA or CTA, indicating the rare codon in this position is significant for the regulation of lmbU expression. Moreover, replacement of TTA codons in both genes with another leucin codon in the bldA mutant did not restore lincomycin production. Thus, we believe that the bldA gene regulates lincomycin production via controlling the translation of not only lmbB2 and lmbU, but also the other TTA-containing genes. In conclusion, the present study demonstrated the importance of the bldA gene in morphological differentiation and lincomycin production in S. lincolnensis.
全局调控因子 BldA 是唯一识别 UUA 这一稀有亮氨酸密码子的 tRNA，其最为人所知的功能是影响链霉菌属的形态分化和次级代谢。在本研究中，我们证实了 bldA 基因（Genbank 登录号 EU124663.1）在链霉菌林肯亚种中的调控功能。bldA 基因的缺失会阻碍孢子形成和林可霉素的产生，而当用功能正常的 bldA 基因进行互补时，这些缺陷可以恢复。Western blotting 分析表明，编码 L-酪氨酸羟化酶的 lmbB2 基因的翻译绝对依赖于 BldA；然而，在 bldA 突变体中观察到编码簇定位调控因子（CSR）的 lmbU 基因发生错译。有趣的是，当使用优选的同义密码子 CTG 时，与使用稀有密码子 TTA 或 CTA 相比，LmbU 的表达水平并非最高，这表明该位置的稀有密码子对于 lmbU 表达的调控具有重要意义。此外，在 bldA 突变体中，用另一个亮氨酸密码子替换这两个基因中的 TTA 密码子并没有恢复林可霉素的产生。因此，我们认为 bldA 基因通过控制不仅 lmbB2 和 lmbU，还控制其他含有 TTA 的基因的翻译来调节林可霉素的产生。总之，本研究表明了 bldA 基因在链霉菌林肯亚种的形态分化和林可霉素产生中的重要性。
