Deinococcus radiodurans PprI Switches on DNA Damage Response and Cellular Survival Networks after Radiation Damage

Abstract

Preliminary findings indicate that PprI is a regulatory protein that stimulates transcription and translation of recA and other DNA repair genes in response to DNA damage in the extremely radioresistant bacterium Deinococcus radiodurans. To define the repertoire of proteins regulated by PprI and investigate the in vivo regulatory mechanism of PprI in response to ␥ radiation, we performed comparative proteomics analyses on wild type (R1) and a pprI knock-out strain ( The Gram-positive nonpathogenic bacterium Deinococcus radiodurans is characterized by extreme resistance to ionizing radiation, UV irradiation, desiccation, and a variety of DNAdamaging agents without resulting in lethality or mutagenesis (1, 2). This dramatic capability is ascribed to its outstanding efficiency in reconstructing a functional genome with high fidelity from hundreds of double strand breaks (DSBs) 1 generated by DNA-damaging agents (2, 3), whereas few other organisms can tolerate DSBs (4). Exponentially growing D. radiodurans is able to withstand 50 -100 times more ionizing radiation than Escherichia coli and can survive a 15-kGy acute ionizing radiation dose with no loss of viability. Its ability of continuous growth without any delay when exposed to a maximum of 60 Gy/h ␥ ray (5) has made it one of the most distinguished candidates for bioremediation of radioactive wastes and contaminants (6, 7). More than 50 years of research has provided many lines of evidence supporting the benefits of the extreme radioresistance of D. radiodurans from its highly efficient DNA damage repair system and its remarkable antioxidation system (1, 8 -15). However, the mechanism underlying its radioresistance is still not completely understood (4, 9). Intriguingly this bacterium not only possesses most of the DNA repair genes found in other organisms but also contains many proteins of yet to be determined functions that have been revealed by genome sequencing and comparative genomics (16,17). These function-unknown proteins may play crucial roles in radioresistance (9, 18) as implied by several studies in this bacterium (19 -23).Several years ago, our group and that of John Battista (19, 22) identified and validated a novel protein, PprI (also named IrrE), essential in D. radiodurans radioresistance. It strongly enhanced catalase activities and promoted the expression of RecA and PprA (19). Expression of the novel gene, driven by the promoter of D. radiodurans groEL (DR0607), also significantly enhanced the resistance of E. coli to ␥ irradiation. We found that the expression of PprI in E. coli also increased the expression of RecA and improved catalase activity (24). Both microarray and Western blotting analysis demonstrated that ionizing radiation did not increase PprI transcription or trans-

Oxidative Stress Resistance inDeinococcus radiodurans

“…Its inactivation provokes a dramatic increase in sensitivity to ionizing radiation, UV radiation, and MMC (170,260) (Fig. 8) and a considerable delay in genome reassembly (377). A constitutively high concentration of RecA (100,000 monomers) can fully restore the resistance of IrrEdeficient bacteria to MMC without any effect on ionizing radiation resistance (277).…”

“…Among the radiation-induced transcriptional regulators, the most highly induced are DdrO (DR2574), belonging to the Xre family of transcriptional regulators (602); IrrI (DR0171), belonging to a specific deinococcal family of transcriptional regulators (368); and DrRRA (DR2418) (677). IrrE (377) and DrRRA (645) control the expression of many genes following ionizing radiation.…”

“…IrrE (170), also referred to as PprI (260), is a novel regulatory protein considered to be a general switch that efficiently enhances the DNA repair capability and the extreme radiation resistance of D. radiodurans via the regulation of a series of pathways (377). Its inactivation provokes a dramatic increase in sensitivity to ionizing radiation, UV radiation, and MMC (170,260) (Fig.…”

Mutagenic lesion bypass and two functionally different RecA proteins in Deinococcus deserti

“…3). The DirrE strain is less tolerant to radiation than the DrecA C DrecAP1 double mutant, probably because IrrE regulates multiple DNA repair and protection pathways (Hua et al, 2003;Lu et al, 2009). Moreover, the DrecAC DrecAP1 strain still contains intact recAP3.…”

“…The products of additional genes specifically conserved in Deinococcus are also involved in DNA repair and radiation tolerance. These include PprA (reported to stimulate ligase activity) (Narumi et al, 2004), DdrA (an oligomeric ring-forming protein involved in DNA extremity protection) (Harris et al, 2004;Gutsche et al, 2008), DdrB, DdrC and DdrD (functions unknown) de Groot et al, 2009) and IrrE (regulator of recA and pprA expression) (Earl et al, 2002a;Hua et al, 2003;Lu et al, 2009;Vujicic-Zagar et al, 2009). Homologues of DNA repair photolyases and specialized translesion synthesis (TLS) DNA polymerases have not been identified in D. radiodurans and D. geothermalis.…”