Regulation of DNA repair genes in cyanobacteria is an unexplored field despite some of them exhibiting high radio-resistance. With RecF pathway speculated to be the major double strand break repair pathway in Nostoc sp. strain PCC7120, regulation of recF, recO and recR genes was investigated. Bioinformatic approach-based identification of promoter and regulatory elements was validated using qRT-PCR analysis, reporter gene and DNA binding assays. Different deletion constructs of the upstream regulatory regions of these genes were analysed in host Nostoc as well as heterologous system Escherichia coli. Studies revealed: (1) Positive regulation of all three genes by NtcA, (2) Negative regulation by LexA, (3) Involvement of contiguous heptamer repeats with/without its yet to be identified interacting partner in regulating (i) binding of NtcA and LexA to recO promoter and its translation, (ii) transcription or translation of recF, (4) Translational regulation of recF and recO through non-canonical and distant S.D. sequence and of recR through a rare initiation codon. Presence of NtcA either precludes binding of LexA to AnLexA-Box or negates its repressive action resulting in higher expression of these genes under nitrogen-fixing conditions in Nostoc. Thus, in Nostoc, expression of recF, recO and recR genes is intricately regulated through multiple regulatory elements/proteins. Contiguous heptamer repeats present across the Nostoc genome in the vicinity of start codon or promoter is likely to have a global regulatory role. This is the first report detailing regulation of DSB repair genes in any algae.

蓝藻中 DNA 修复基因的调控是一个未开发的领域，尽管其中一些表现出高抗辐射性。据推测，RecF 通路是Nostoc sp. 中主要的双链断裂修复通路。菌株 PCC7120，研究了recF、recO和recR基因的调节。使用 qRT-PCR 分析、报告基因和 DNA 结合分析验证了基于生物信息学方法的启动子和调控元件鉴定。在宿主发菜和异源系统大肠杆菌中分析了这些基因上游调节区的不同缺失结构. 研究表明：(1) NtcA 对所有三个基因的正调控，(2) LexA 的负调控，(3) 连续七聚体重复序列的参与，有/没有其尚未确定的相互作用伙伴调节 (i) NtcA 的结合和LexA 到recO启动子及其翻译，(ii) recF的转录或翻译，(4)通过非规范和远距离 SD 序列对recF和recO的翻译调节，以及通过稀有起始密码子对recR的翻译调节。NtcA 的存在要么阻止 LexA 与 AnLexA-Box 的结合，要么否定其抑制作用，导致这些基因在发菜固氮条件下的更高表达。因此，在发菜, recF、recO和recR基因的表达通过多种调节元件/蛋白质进行复杂调节。在起始密码子或启动子附近的念珠菌基因组中存在的连续七聚体重复序列可能具有全局调节作用。这是第一份详细说明任何藻类中 DSB 修复基因调控的报告。