It has been shown [1,2] that the following glycosyl hydrolases can be classified into a single family on the basis of sequence similarities:

• Inulinase (EC 3.2.1.7) (or inulase) from the fungi Kluyveromyces marxianus.
• β-fructofuranosidase (EC 3.2.1.26), commonly known as invertase in fungi and plants and as sucrase in bacteria (gene sacA or scrB).
• Raffinose invertase (EC 3.2.1.26) (gene rafD) from Escherichia coli plasmid pRSD2.
• Levanase (EC 3.2.1.65) (gene sacC) from Bacillus subtilis.

One of the conserved regions in these enzymes is located in the N-terminal section and contains an aspartic acid residue which has been shown [3], in yeast invertase to be important for the catalytic mechanism. We have used this region as a signature pattern.