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

Abstract

Using the pIJ702 vector, a xylanase-encoding gene (xln) of Streptomyces sp. EC3 has been cloned by functional complementation of a mutant of Sfrepfomyces lividans TK24, producing xy-lanase 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 Sstl 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 Strepfomyces xylanase genes. The xylanase aa sequence showed a clear homology with the aa sequences of other xy-lanases of the glycanase C 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 COR sequence of the absence of a regulatory system.

Key Words:

• Regulatory protein
• Streptomyces
• xylanase cloning
• xylanase-negative mutant