División de Genética and.
Departamento de Matemática Aplicada, Universidad de Alicante, 03080 Alicante, Spain;
Proc Natl Acad Sci U S A. 2014 Jun 10;111(23):E2423-30. doi: 10.1073/pnas.1404097111. Epub 2014 May 27.
To modulate the expression of genes involved in nitrogen assimilation, the cyanobacterial PII-interacting protein X (PipX) interacts with the global transcriptional regulator NtcA and the signal transduction protein PII, a protein found in all three domains of life as an integrator of signals of the nitrogen and carbon balance. PipX can form alternate complexes with NtcA and PII, and these interactions are stimulated and inhibited, respectively, by 2-oxoglutarate, providing a mechanistic link between PII signaling and NtcA-regulated gene expression. Here, we demonstrate that PipX is involved in a much wider interaction network. The effect of pipX alleles on transcript levels was studied by RNA sequencing of S. elongatus strains grown in the presence of either nitrate or ammonium, followed by multivariate analyses of relevant mutant/control comparisons. As a result of this process, 222 genes were classified into six coherent groups of differentially regulated genes, two of which, containing either NtcA-activated or NtcA-repressed genes, provided further insights into the function of NtcA-PipX complexes. The remaining four groups suggest the involvement of PipX in at least three NtcA-independent regulatory pathways. Our results pave the way to uncover new regulatory interactions and mechanisms in the control of gene expression in cyanobacteria.
为了调节参与氮同化的基因表达，蓝细菌 PII 相互作用蛋白 X（PipX）与全局转录调节因子 NtcA 和信号转导蛋白 PII 相互作用，PII 作为氮碳平衡信号的整合因子存在于所有三个生命领域。PipX 可以与 NtcA 和 PII 形成交替复合物，这些相互作用分别被 2-氧戊二酸刺激和抑制，为 PII 信号和 NtcA 调节的基因表达之间提供了一个机制联系。在这里，我们证明 PipX 参与了一个更广泛的相互作用网络。通过在硝酸盐或铵存在下生长的 S. elongatus 菌株的 RNA 测序研究 pipX 等位基因对转录水平的影响，然后对相关突变体/对照比较进行多元分析。作为这一过程的结果，222 个基因被分类为六个有差异调节基因的连贯组，其中两个组分别包含 NtcA 激活或 NtcA 抑制的基因，为 NtcA-PipX 复合物的功能提供了进一步的见解。其余四个组表明 PipX 至少参与了三个 NtcA 独立的调控途径。我们的结果为揭示蓝细菌基因表达调控中的新的调控相互作用和机制铺平了道路。
