The trp RNA-binding attenuation protein (TRAP) regulates expression of the Bacillus subtilis trpEDCFBA operon by transcription attenuation and translational control mechanisms. Both mechanisms require binding of tryptophan-activated TRAP to 11 (G/U)AG repeats in the trp leader transcript. trpE translational control involves formation of a TRAP-dependent RNA structure that sequesters the trpE Shine-Dalgarno (SD) sequence (the SD blocking hairpin). By comparing expression levels from trpE'-'lacZ translational fusions controlled by the wild-type leader or by a leader that cannot form the SD blocking hairpin, we found that translational control requires a tryptophan concentration higher than that required for transcription attenuation. We also found that inhibition of trpE translation by the SD blocking hairpin does not alter the stability of the downstream message. Since the coding sequences for trpE and trpD overlap by 29 nucleotides, we examined expression levels from trpED'-'lacZ translational fusions to determine if these two genes are translationally coupled. We found that introduction of a UAA stop codon in trpE resulted in a substantial reduction in expression. Since expression was partially restored in the presence of a tRNA suppressor, our results indicate that trpE and trpD are translationally coupled. We determined that the coupling mechanism is TRAP independent and that formation of the SD blocking hairpin regulates trpD translation via translational coupling. We also constructed a rho mutation to investigate the role of Rho-dependent termination in trp operon expression. We found that TRAP-dependent formation of the SD blocking hairpin allows Rho access to the nascent transcript, causing transcriptional polarity.

译文

trp RNA结合衰减蛋白 (TRAP) 通过转录衰减和翻译控制机制调节枯草芽孢杆菌trpEDCFBA操纵子的表达。两种机制都需要色氨酸激活的TRAP与trp前导转录物中的11个 (G/U)AG重复序列结合。trpE翻译控制包括形成依赖于trpE Shine-Dalgarno (SD) 序列 (SD阻断发夹) 的RNA结构。通过比较trpE的表达水平-由野生型领导者或不能形成SD阻塞发夹的领导者控制的lacz翻译融合,我们发现翻译控制需要比转录衰减所需的色氨酸浓度更高。我们还发现SD阻断发夹对trpE翻译的抑制不会改变下游信息的稳定性。由于trpE和trpD的编码序列重叠了29个核苷酸,我们检查了trpED'-'lacZ翻译融合的表达水平,以确定这两个基因是否在翻译上耦合。我们发现在trpE中引入UAA终止密码子导致了表达的大幅降低。由于在tRNA抑制剂的存在下部分恢复了表达,我们的结果表明trpE和trpD是翻译耦合的。我们确定耦合机制是陷阱独立的,并且SD阻断发夹的形成通过翻译耦合调节trpD翻译。我们还构建了一个rho突变来研究Rho依赖性终止在trp操纵子表达中的作用。我们发现陷阱-SD阻塞发夹的依赖形成使Rho可以访问新生的转录本,导致转录极性。

+1
+2
100研值 100研值 ¥99课程
检索文献一次
下载文献一次

去下载>

成功解锁2个技能,为你点赞

《SCI写作十大必备语法》
解决你的SCI语法难题!

技能熟练度+1

视频课《玩转文献检索》
让你成为检索达人!

恭喜完成新手挑战

手机微信扫一扫,添加好友领取

免费领《Endnote文献管理工具+教程》

微信扫码, 免费领取

手机登录

获取验证码
登录