Li Xin, Sandh Gustaf, Nenninger Anja, Muro-Pastor Alicia M, Stensjö Karin
Microbial Chemistry, Department of Chemistry - Ångström Laboratory, Science for Life Laboratory, Uppsala University, Box 523, SE-751 20 Uppsala, Sweden.
Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas and Universidad de Sevilla, E-41092 Seville, Spain.
FEMS Microbiol Lett. 2015 Mar;362(6). doi: 10.1093/femsle/fnv017. Epub 2015 Feb 5.
In cyanobacteria, DNA-binding proteins from starved cells (Dps) play an important role in the cellular response to oxidative and nutritional stresses. In this study, we have characterized the cell-type specificity and the promoter regions of two orthologous dps genes, Npun_R5799 in Nostoc punctiforme and alr3808 in Anabaena sp. PCC 7120. A transcriptional start site (TSS), identical in location to the previously identified proximal TSS of alr3808, was identified for Npun_R5799 under both combined nitrogen supplemented and N2-fixing growth conditions. However, only alr3808 was also transcribed from a second distal TSS. Sequence homologies suggest that the promoter region containing the distal TSS is not conserved upstream of orthologous genes among heterocyst-forming cyanobacteria. The analysis of promoter GFP-reporter strains showed a different role in governing cell-type specificity between the proximal and distal promoter of alr3808. We here confirmed the heterocyst specificity of the distal promoter of alr3808 and described a very early induction of its expression during proheterocyst differentiation. In contrast, the complete promoters of both genes were active in all cells. Even though Npun_R5799 and alr3808 are orthologs, the regulation of their respective expression differs, indicating distinctions in the function of these cyanobacterial Dps proteins depending on the strain and cell type.
在蓝细菌中，饥饿细胞的DNA结合蛋白（Dps）在细胞对氧化应激和营养应激的反应中发挥重要作用。在本研究中，我们对两个直系同源dps基因的细胞类型特异性和启动子区域进行了表征，这两个基因分别是点状念珠藻中的Npun_R5799和鱼腥藻PCC 7120中的alr3808。在添加联合氮源和固氮生长条件下，均为Npun_R5799鉴定到一个转录起始位点（TSS），其位置与先前鉴定的alr3808近端TSS相同。然而，只有alr3808也从第二个远端TSS转录。序列同源性表明，在形成异形胞的蓝细菌中，含有远端TSS的启动子区域在直系同源基因上游并不保守。启动子GFP报告菌株的分析表明，alr3808的近端和远端启动子在控制细胞类型特异性方面具有不同作用。我们在此证实了alr3808远端启动子的异形胞特异性，并描述了其在原异形胞分化过程中非常早期的表达诱导。相比之下，这两个基因的完整启动子在所有细胞中均有活性。尽管Npun_R5799和alr3808是直系同源基因，但它们各自的表达调控有所不同，这表明这些蓝细菌Dps蛋白的功能因菌株和细胞类型而异。
