Summary: Endoxylanase () and β-xylosidase () genes from were subcloned from a cosmid clone (pXDM1) to generate pXPH3. The nucleotide sequence of a I-dIII fragment in pXPH3 that contained revealed an open reading frame (ORF) of 1500 bp encoding a 55 kDa protein. Another open reading frame (ORF1) of unknown function was found 21 bp downstream from the first stop codon of , ORF1 and had the same direction of transcription. from strain B6A-RI exhibited 45% amino acid similarity, with 18% amino acid identity to of strain B6A-RI, and 61% similarity and 37% identity with the β-xylosidase gene from Recombinant β-xylosidase was purified from (pXPH3) cells. The enzyme was a monomer with a molecular mass of 55 kDa. The specific activity and pH and temperature optima for hydrolysis of -nitrophenyl-β-D-xylopyranoside (pNPX) were 5.53 U mg, 5.5 and 70 °C, respectively. The β-xylosidase was stable at 65 °C, but lost activity at 85 °C. The purified enzyme had hydrolytic activity towards xylopentose, xylotriose, xylobiose and pNPX, but had no activity toward xylan.


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