Cloning and nucleotide sequence of a xylanase-encoding gene from Streptomyces sp. strain EC3

Using the p1J702 vector, a xylanase-encoding gene (xin) of Streptomyces sp. EC3 has been cloned by functional complementation of a mutant of Streptomyces lividans TK24, producing xylanase at a very low level. Normal level of xylanase synthesis was restored in at least three clones, containing the same 3802 bp Sstl DNA fragment. In this fragment, several open reading frames (ORFs) have been identified, one of which coded for a xylanase; the products of the other ORFs did not show homology with any of the already known proteins. The complete nucleotide sequence of the 3802 bp Ssti insert has been determined on both strands. Xylanase is very probably synthesized as a 240 amino acid (aa) precursor (25949 Da) including a long (49 aa) signal sequence presenting significant similarity with the signal sequences of other Streptomyces xylanase genes. The xylanase aa sequence showed a clear homology with the aa sequences of other xylanases of the glycanase G family. The xln gene has been introduced into Streptomyces parvulus, a naturally xylanase-negative species. In contrast with its expression in Streptomyces sp. EC3, in S. parvulus, xln was expressed constitutively, a probable consequence of the absence of a regulatory system.