Department of Biology, Stanford University, Stanford, CA 94305, USA.
J Bacteriol. 2010 Mar;192(6):1518-26. doi: 10.1128/JB.01420-09. Epub 2010 Jan 8.
Tryptophan, phenylalanine, tyrosine, and several other metabolites are all synthesized from a common precursor, chorismic acid. Since tryptophan is a product of an energetically expensive biosynthetic pathway, bacteria have developed sensing mechanisms to downregulate synthesis of the enzymes of tryptophan formation when synthesis of the amino acid is not needed. In Bacillus subtilis and some other Gram-positive bacteria, trp operon expression is regulated by two proteins, TRAP (the tryptophan-activated RNA binding protein) and AT (the anti-TRAP protein). TRAP is activated by bound tryptophan, and AT synthesis is increased upon accumulation of uncharged tRNA(Trp). Tryptophan-activated TRAP binds to trp operon leader RNA, generating a terminator structure that promotes transcription termination. AT binds to tryptophan-activated TRAP, inhibiting its RNA binding ability. In B. subtilis, AT synthesis is upregulated both transcriptionally and translationally in response to the accumulation of uncharged tRNA(Trp). In this paper, we focus on explaining the differences in organization and regulatory functions of the at operon's leader peptide-coding region, rtpLP, of B. subtilis and Bacillus licheniformis. Our objective was to correlate the greater growth sensitivity of B. licheniformis to tryptophan starvation with the spacing of the three Trp codons in its at operon leader peptide-coding region. Our findings suggest that the Trp codon location in rtpLP of B. licheniformis is designed to allow a mild charged-tRNA(Trp) deficiency to expose the Shine-Dalgarno sequence and start codon for the AT protein, leading to increased AT synthesis.
色氨酸、苯丙氨酸、酪氨酸和其他几种代谢物均由一个共同的前体——邻氨基苯甲酸合成。由于色氨酸是一个能量消耗很大的生物合成途径的产物，细菌已经开发出感应机制，当不需要合成氨基酸时，下调色氨酸形成酶的合成。在枯草芽孢杆菌和其他一些革兰氏阳性菌中，trp 操纵子的表达受两种蛋白质 TRAP（色氨酸激活的 RNA 结合蛋白）和 AT（抗 TRAP 蛋白）的调节。TRAP 被结合的色氨酸激活，当无电荷 tRNA（Trp）积累时，AT 的合成增加。色氨酸激活的 TRAP 结合到 trp 操纵子的前导 RNA 上，生成一个终止子结构，促进转录终止。AT 结合到色氨酸激活的 TRAP 上，抑制其 RNA 结合能力。在枯草芽孢杆菌中，AT 的合成在转录和翻译水平上均被上调，以响应无电荷 tRNA（Trp）的积累。在本文中，我们重点解释枯草芽孢杆菌和地衣芽孢杆菌的 at 操纵子前导肽编码区 rtpLP 的组织和调节功能的差异。我们的目的是将地衣芽孢杆菌对色氨酸饥饿的生长敏感性与它的 at 操纵子前导肽编码区中三个色氨酸密码子的间隔联系起来。我们的发现表明，地衣芽孢杆菌 rtpLP 中的 Trp 密码子位置设计为允许轻度带电荷的 tRNA（Trp）缺乏暴露 AT 蛋白的 Shine-Dalgarno 序列和起始密码子，从而增加 AT 的合成。
