The　lysine　(K)　tRNA　synthetase　C-terminal　(KTSC)　domain　containing　proteins　are　widely　spread　in　Bacteria,　Archaea　and　Viruses,　but　the　function　of　this　short　domain　is　unclear.　The　occurrence　of　the　fusion　of　KTSC　domain　to　a　catalytic　domain　or　domains　related　to　DNA　or　RNA　metabolisms　suggests　its　potential　role　in　DNA　or　RNA　binding.　Here,　we　report　the　characterization　of　Mvu8s　from　Methanolobus　vulcani,　which　consists　of　a　single　KTSC　domain.　Mvu8s　binds　specifically　to　ssDNA　with　an　affinity　approximately　40-and　10-fold　higher　than　those　for　dsDNA　and　ssRNA　in　vitro,　respectively.　It　shows　a　slight　preference　to　the　G-rich　DNA　sequence　but　barely　binds　the　A-stretch.　Crystal　structure　of　Mvu8s　shows　that　it　forms　a　homo-tetramer,　with　each　monomer　composed　of　a　four-strand　antiparallel　13-sheet　and　a　helix-turn-helix　in　the　order　of　131-132-133-alpha　1-alpha　2-134.　Four　basic　residues　(R3,　R7,　K54　and　K58)　were　found　to　serve　important　roles　in　ssDNA-binding.　And,　the　spiral　arrangement　of　the　DNA　interfaces　in　Mvu8s　homo-tetramer　presumably　results　in　ssDNA　wrapping.　Our　results　not　only　offer　clues　of　the　functions　of　the　KTSC　domain　containing　proteins　but　also　expand　our　knowledge　on　the　non-oligonucleotide-binding　(OB)　fold　single-stranded　DNA-binding　proteins　in　Archaea.