LexA protein of cyanobacterium Anabaena sp. strain PCC7120 exhibits in vitro pH-dependent and RecA-independent autoproteolytic activity

Kumar, Arvind; Kirti, Anurag; Rajaram, Hema

doi:10.1016/j.biocel.2014.12.003

Cited by 19 publications

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“…Interestingly, the Synechocystis PCC6803 lexA gene appeared to regulate carbon assimilation (Domain et al, 2004) and cell motility (Kizawa et al, 2016), but not DNA recombination and repair (Domain et al, 2004). Furthermore, the Nostoc PCC7120 LexA protein has a RecA-independent autoproteolytic cleavage (Kumar et al, 2015). …”

Section: Resultsmentioning

confidence: 99%

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Comparative Genomics of DNA Recombination and Repair in Cyanobacteria: Biotechnological Implications

2016

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Cyanobacteria are fascinating photosynthetic prokaryotes that are regarded as the ancestors of the plant chloroplast; the purveyors of oxygen and biomass for the food chain; and promising cell factories for an environmentally friendly production of chemicals. In colonizing most waters and soils of our planet, cyanobacteria are inevitably challenged by environmental stresses that generate DNA damages. Furthermore, many strains engineered for biotechnological purposes can use DNA recombination to stop synthesizing the biotechnological product. Hence, it is important to study DNA recombination and repair in cyanobacteria for both basic and applied research. This review reports what is known in a few widely studied model cyanobacteria and what can be inferred by mining the sequenced genomes of morphologically and physiologically diverse strains. We show that cyanobacteria possess many E. coli-like DNA recombination and repair genes, and possibly other genes not yet identified. E. coli-homolog genes are unevenly distributed in cyanobacteria, in agreement with their wide genome diversity. Many genes are extremely well conserved in cyanobacteria (mutMS, radA, recA, recFO, recG, recN, ruvABC, ssb, and uvrABCD), even in small genomes, suggesting that they encode the core DNA repair process. In addition to these core genes, the marine Prochlorococcus and Synechococcus strains harbor recBCD (DNA recombination), umuCD (mutational DNA replication), as well as the key SOS genes lexA (regulation of the SOS system) and sulA (postponing of cell division until completion of DNA reparation). Hence, these strains could possess an E. coli-type SOS system. In contrast, several cyanobacteria endowed with larger genomes lack typical SOS genes. For examples, the two studied Gloeobacter strains lack alkB, lexA, and sulA; and Synechococcus PCC7942 has neither lexA nor recCD. Furthermore, the Synechocystis PCC6803 lexA product does not regulate DNA repair genes. Collectively, these findings indicate that not all cyanobacteria have an E. coli-type SOS system. Also interestingly, several cyanobacteria possess multiple copies of E. coli-like DNA repair genes, such as Acaryochloris marina MBIC11017 (2 alkB, 3 ogt, 7 recA, 3 recD, 2 ssb, 3 umuC, 4 umuD, and 8 xerC), Cyanothece ATCC51142 (2 lexA and 4 ruvC), and Nostoc PCC7120 (2 ssb and 3 xerC).

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Section: Resultsmentioning

confidence: 99%

“…Similarly, no SOS box was found in the promoter region of the Synechococcus PCC7002 recA gene (Murphy et al, 1990). Furthermore, the lexA gene of Anabaena PCC7120 was neither induced by UV-B nor mitomycin C. In addition, the Synechocystis PCC6803 LexA protein has a RecA-independent autoproteolytic cleavage (Kumar et al, 2015). …”

Section: Resultsmentioning

confidence: 99%

Comparative Genomics of DNA Recombination and Repair in Cyanobacteria: Biotechnological Implications

2016

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“…The absence of activated RecA‐dependent cleavage of Anabaena LexA both in vitro and in vivo (Kumar et al. ) accounts for the lack of change in expression of P ssb1 and P ssb2 . The low levels of expression of LexA in Anabaena (Kumar et al.…”

Section: Discussionmentioning

confidence: 99%

“…The low levels of expression of LexA in Anabaena (Kumar et al. ), and the comparatively lower binding affinity of Anabaena LexA to the two promoters, as indicated by the higher concentration of the protein required for mobility shift (Fig. a), ensure that the two genes are not repressed in Anabaena , since both are essential based on the nonviability of their deletion mutants (Kirti et al.…”

Section: Discussionmentioning

confidence: 99%

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Differential regulation of ssb genes in the nitrogen‐fixing cyanobacterium, Anabaena sp. strain PCC7120¹

Kirti

Kumar

Rajaram

2017

Journal of Phycology

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Anabaena sp. PCC7120 possesses three genes coding for single-stranded DNA-binding (SSB) protein, of which ssb1 was a single gene, and ssb2 and ssb3 are the first genes of their corresponding operons. Regulation of the truncated ssb genes, ssb1 (alr0088) and ssb2 (alr7559), was unaffected by N-status of growth. They were negatively regulated by the SOS-response regulatory protein LexA, as indicated by the (i) binding of Anabaena LexA to the LexA box of regulatory regions of ssb1 and ssb2, and (ii) decreased expression of the downstream gfp reporter gene in Escherichia coli upon co-expression of LexA. However, the full-length ssb gene, ssb3 (all4779), was regulated by the availability of Fe and combined nitrogen, as indicated by (i) increase in the levels of SSB3 protein on Fe -depletion and decrease under Fe -excess conditions, and (ii) 1.5- to 1.6-fold decrease in activity under nitrogen-fixing conditions compared to nitrogen-supplemented conditions. The requirement of Fe as a co-factor for repression by FurA and the increase in levels of FurA under nitrogen-deficient conditions in Anabaena (Lopez-Gomollon et al. 2007) indicated a possible regulation of ssb3 by FurA. This was substantiated by (i) the binding of FurA to the regulatory region of ssb3, (ii) repression of the expression of the downstream gfp reporter gene in E. coli upon co-expression of FurA, and (iii) negative regulation of ssb3 promoter activity by the upstream AT-rich region in Anabaena. This is the first report on possible role of FurA, an important protein for iron homeostasis, in DNA repair of cyanobacteria.

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The SbcC and SbcD homologs of the cyanobacterium Anabaena sp. strain PCC7120 (Alr3988 and All4463) contribute independently to DNA repair

Pandey

Kirti

Kumar

et al. 2018

Funct Integr Genomics

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The ubiquitous SbcCD exonuclease complex has been shown to perform an important role in DNA repair across prokaryotes and eukaryotes. However, they have remained uncharacterized in the ancient and stress-tolerant cyanobacteria. In the cyanobacterium Anabaena sp. strain PCC7120, SbcC and SbcD homologs, defined on the basis of the presence of corresponding functional domains, are annotated as hypothetical proteins, namely Alr3988 and All4463 respectively. Unlike the presence of sbcC and sbcD genes in a bicistronic operon in most organisms, these genes were distantly placed on the chromosome in Anabaena, and found to be negatively regulated by LexA. Both the genes were found to be essential in Anabaena as the individual deletion mutants were non-viable. On the other hand, the proteins could be individually overexpressed in Anabaena with no effect on normal cell physiology. However, they contributed positively to enhance the tolerance to different DNA damage-inducing stresses, such as mitomycin C and UV- and γ-radiation. This indicated that the two proteins, at least when overexpressed, could function independently and mitigate the damage caused due to the formation of DNA adducts and single- and double-strand breaks in Anabaena. This is the first report on possible independent in vivo functioning of SbcC and SbcD homologs in any bacteria, and the first effort to functionally characterize the proteins in any cyanobacteria.

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LexA protein of cyanobacterium Anabaena sp. strain PCC7120 exhibits in vitro pH-dependent and RecA-independent autoproteolytic activity

Cited by 19 publications

References 32 publications

Comparative Genomics of DNA Recombination and Repair in Cyanobacteria: Biotechnological Implications

Comparative Genomics of DNA Recombination and Repair in Cyanobacteria: Biotechnological Implications

Differential regulation of ssb genes in the nitrogen‐fixing cyanobacterium, Anabaena sp. strain PCC7120¹

The SbcC and SbcD homologs of the cyanobacterium Anabaena sp. strain PCC7120 (Alr3988 and All4463) contribute independently to DNA repair

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LexA protein of cyanobacterium Anabaena sp. strain PCC7120 exhibits in vitro pH-dependent and RecA-independent autoproteolytic activity

Cited by 19 publications

References 32 publications

Comparative Genomics of DNA Recombination and Repair in Cyanobacteria: Biotechnological Implications

Comparative Genomics of DNA Recombination and Repair in Cyanobacteria: Biotechnological Implications

Differential regulation of ssb genes in the nitrogen‐fixing cyanobacterium, Anabaena sp. strain PCC71201

The SbcC and SbcD homologs of the cyanobacterium Anabaena sp. strain PCC7120 (Alr3988 and All4463) contribute independently to DNA repair

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Differential regulation of ssb genes in the nitrogen‐fixing cyanobacterium, Anabaena sp. strain PCC7120¹