Abstract
BackgroundDeinococcus radiodurans R1 is one of the most radiation-resistant organisms known and is able to repair an unusually large amount of DNA damage without induced mutation. Single-stranded DNA-binding (SSB) protein is an essential protein in all organisms and is involved in DNA replication, recombination and repair. The published genomic sequence from Deinococcus radiodurans includes a putative single-stranded DNA-binding protein gene (ssb; DR0100) requiring a translational frameshift for synthesis of a complete SSB protein. The apparently tripartite gene has inspired considerable speculation in the literature about potentially novel frameshifting or RNA editing mechanisms. Immediately upstream of the ssb gene is another gene (DR0099) given an ssb-like annotation, but left unexplored.ResultsA segment of the Deinococcus radiodurans strain R1 genome encompassing the ssb gene has been re-sequenced, and two errors involving omitted guanine nucleotides have been documented. The corrected sequence incorporates both of the open reading frames designated DR0099 and DR0100 into one contiguous ssb open reading frame (ORF). The corrected gene requires no translational frameshifts and contains two predicted oligonucleotide/oligosaccharide-binding (OB) folds. The protein has been purified and its sequence is closely related to the Thermus thermophilus and Thermus aquaticus SSB proteins. Like the Thermus SSB proteins, the SSBDr functions as a homodimer. The Deinococcus radiodurans SSB homodimer stimulates Deinococcus radiodurans RecA protein and Escherichia coli RecA protein-promoted DNA three-strand exchange reactions with at least the same efficiency as the Escherichia coli SSB homotetramer.ConclusionsThe correct Deinococcus radiodurans ssb gene is a contiguous open reading frame that codes for the largest bacterial SSB monomer identified to date. The Deinococcus radiodurans SSB protein includes two OB folds per monomer and functions as a homodimer. The Deinococcus radiodurans SSB protein efficiently stimulates Deinococcus radiodurans RecA and also Escherichia coli RecA protein-promoted DNA strand exchange reactions. The identification and purification of Deinococcus radiodurans SSB protein not only allows for greater understanding of the SSB protein family but provides an essential yet previously missing player in the current efforts to understand the extraordinary DNA repair capacity of Deinococcus radiodurans.
Highlights
Deinococcus radiodurans R1 is one of the most radiation-resistant organisms known and is able to repair an unusually large amount of DNA damage without induced mutation
We report that the ssb sequences as originally published include two errors that render the gene interpretation opaque
The D. radiodurans ssb gene encodes a contiguous open reading frame (ORF) The region encompassing the ssb gene, which is flanked by DR0098, the ribosomal protein S6 gene and DR0101, the ribosomal protein S18 gene, was PCR amplified from genomic DNA and sequenced (Fig. 1)
Summary
Deinococcus radiodurans R1 is one of the most radiation-resistant organisms known and is able to repair an unusually large amount of DNA damage without induced mutation. Singlestranded DNA-binding (SSB) protein is an essential protein in all organisms and is involved in DNA replication, recombination and repair. D. radiodurans is able to sustain growth without induced mutation in the presence of considerable levels of ambient radiation (6 krads/h) [2]. This organism possesses a robust DNA damage repair system. Singlestranded DNA-binding protein (SSB) is an essential protein in all known organisms and is required for DNA replication, recombination and repair [3]
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