A　novel　multi-domain　high　molecular　xylanase　coding　gene　(xynSL3)　was　cloned　from　Alkalibacterium　sp.　SL3,　an　alkaliphilic　bacterial　strain　isolated　from　the　sediment　of　soda　lake　Dabusu.　The　deduced　XynSL3　is　composed　of　a　putative　signal　peptide,　three　tandem　domains　of　carbohydrate　binding　module　(CBM)　family　22,　a　catalytic　domain　of　glycosyl　hydrolase　(GH)　family　10　and　a　domain　of　CBM9.　XynSL3　shares　the　highest　identity　of　66%　to　a　hypothetical　protein　from　Alkalibacterium　sp.　AK22　and　has　low　identities　(33-45%)　with　other　functionally　characterized　xylanases.　The　gene　xynSL3　was　expressed　heterologously　in　Escherichia　coli　and　the　recombinant　enzyme　demonstrated　some　particular　characteristics.　Purified　recombinant　XynSL3　(rXynSL3)　was　highly　active　and　stable　over　the　neutral　and　alkaline　pH　ranges　from　7.0　to　12.0,　with　maximum　activity　at　pH　9.0　and　around　45%　activity　at　pH　12.0.　It　had　an　apparent　temperature　optimum　of　55°C　and　was　stable　at　50°C.　The　rXynSL3　was　highly　halotolerant,　retaining　more　than　60%　activity　with　3　M　NaCl　and　was　stable　at　up　to　a　4　M　concentration　of　NaCl.　The　hydrolysis　products　of　rXynSL3　from　corncob　xylan　were　mainly　xylobiose　and　xylotetraose.　The　activity　of　rXynSL3　was　enhanced　by　Ca2+　and　it　has　strong　resistance　to　sodium　dodecyl　sulfate　(SDS).　This　multi-domain,　alkaline　and　salt-tolerant　enzyme　has　great　potential　for　basic　research　and　industrial　applications　such　as　the　biobleaching　of　paper　pulp　and　production　of　xylo-oligosaccharides　(XOS).　©　2017　Wang,　Wu,　Yan,　Lin　and　Ye.