The microbial degradation of cellulose and xylans requires several types of enzymes such as endoglucanases (EC 3.2.1.4), cellobiohydrolases (EC 3.2.1.91) (exoglucanases), or xylanases (EC 3.2.1.8) [1,2]. Fungi and bacteria produces a spectrum of cellulolytic enzymes (cellulases) and xylanases which, on the basis of sequence similarities, can be classified into families. One of these families is known as the cellulase family G [3] or as the glycosyl hydrolases family 11 [4,E1]. The enzymes which are currently known to belong to this family are listed below.

• Aspergillus awamori xylanase C (xynC).
• Bacillus circulans, pumilus, stearothermophilus and subtilis xylanase (xynA).
• Clostridium acetobutylicum xylanase (xynB).
• Clostridium stercorarium xylanase A (xynA).
• Fibrobacter succinogenes xylanase C (xynC) which consist of two catalytic domains that both belong to family 10.
• Neocallimastix patriciarum xylanase A (xynA).
• Ruminococcus flavefaciens bifunctional xylanase XYLA (xynA). This protein consists of three domains: a N-terminal xylanase catalytic domain that belongs to family 11 of glycosyl hydrolases; a central domain composed of short repeats of Gln, Asn an Trp, and a C-terminal xylanase catalytic domain that belongs to family 10 of glycosyl hydrolases.
• Schizophyllum commune xylanase A.
• Streptomyces lividans xylanases B (xlnB) and C (xlnC).
• Trichoderma reesei xylanases I and II.

Two of the conserved regions in these enzymes are centered on glutamic acid residues which have both been shown [5], in Bacillus pumilis xylanase, to be necessary for catalytic activity. We have used both regions as signature patterns.