Life Science Research Center, College of Bioresource Sciences, Nihon University, Kanagawa, Japan.
Life Science Research Center, College of Bioresource Sciences, Nihon University, Kanagawa, Japan
J Bacteriol. 2018 Nov 26;200(24). doi: 10.1128/JB.00285-18. Print 2018 Dec 15.
The LitR/CarH protein family is an adenosyl B (AdoB)-dependent photoreceptor family with DNA-binding activity, and its homologs are widely distributed in the genomes of diverse bacterial genera. In this investigation, we studied the role and functions of a LitR homolog from a Gram-negative soil bacterium, , which does not possess an AdoB-binding domain. Transcriptome analysis indicated the existence of 19 light-induced genes, including , , , photolyase gene , and , located in the region flanking Disruption of caused constitutive expression of all the light-inducible genes, while mutation in the light-induced sigma factor gene, , abolished the transcription of the operon and the operon, indicating that LitR and LitS play a central role in light-inducible transcription. A gel shift assay showed that recombinant protein LitR specifically binds to the promoter regions of and the operon, and its binding was weakened by UV-A illumination. LitR absorbs light at maximally near 340 nm and exhibited a photocyclic response and light-dependent dissociation of multimer into tetramer. The mutant produced a 20-fold-higher intracellular level of folate than that of the wild-type strain. Thus, the evidence suggests that LitR light-dependently regulates the transcription of itself and the operon, resulting in the production of folate, and then the expressed RNA polymerase complex containing σ directs the transcription of the operon and the operon. These light-dependent characteristics suggest that class III LitR, in complex with a UV-A-absorbing molecule, follows a novel light-sensing mechanism. Members of the LitR/CarH family are adenosyl B-based photosensory transcriptional regulator involved in light-inducible carotenoid production in nonphototrophic bacteria. Our study provides the first evidence of the involvement of a class III LitR, which lacks an adenosyl B-binding domain in the light response of belonging to betaproteobacteria. Our biochemical analysis suggests that class III LitR protein exhibits features as a photosensor including absorption of light at the UV-A region (λ = ca. 340 nm), photocyclic response, and light-dependent dissociation. This suggests that class III LitR associates with a UV-A-absorbing molecule, and it has a photosensing mechanism distinguishable from that of the B-based type.
LitR/CarH 蛋白家族是一种依赖腺苷 B（AdoB）的光感受器家族，具有 DNA 结合活性，其同源物广泛分布于各种细菌属的基因组中。在这项研究中，我们研究了革兰氏阴性土壤细菌中的 LitR 同源物的作用和功能，该同源物不具有 AdoB 结合结构域。转录组分析表明，存在 19 个光诱导基因，包括 、 、 、光解酶基因 以及位于侧翼的 。 破坏导致所有光诱导基因的组成型表达，而在光诱导 sigma 因子基因 中突变， ，则转录 操纵子和 操纵子，表明 LitR 和 LitS 在光诱导转录中起核心作用。凝胶迁移分析表明，重组蛋白 LitR 特异性结合 和 操纵子的启动子区域，其结合通过 UV-A 照射而减弱。LitR 在最大近 340nm 处吸收光，并表现出光循环反应和光依赖性多聚体解离为四聚体。 突变体比野生型菌株产生高 20 倍的叶酸。因此，证据表明 LitR 依赖光调节自身和 操纵子的转录，从而产生叶酸，然后含有 σ 的表达 RNA 聚合酶复合物指导 操纵子和 操纵子的转录。这些光依赖性特征表明，III 类 LitR 与吸收 UV-A 的分子一起遵循一种新的光感测机制。LitR/CarH 家族的成员是基于腺苷 B 的光敏转录调节剂，参与非光合细菌中光诱导类胡萝卜素的产生。我们的研究首次提供了证据，表明缺乏腺苷 B 结合结构域的 III 类 LitR 参与了属于β变形杆菌的 的光反应。我们的生化分析表明，III 类 LitR 蛋白表现出作为光传感器的特征，包括在 UV-A 区域（λ≈340nm）吸收光、光循环反应和光依赖性解离。这表明 III 类 LitR 与吸收 UV-A 的分子相关，并且具有与基于 B 的类型不同的光感测机制。
