NOVELTY - A transformant of yeast (Schizosaccharomyces) comprising promoter sequence and terminator sequence for making structural gene to express as an extrachromosomal gene in a chromosome, is new. The structural gene sequence includes a region which encodes modified beta -glucosidase. The beta -glucosidase has thermal stability or glucose inhibition tolerance.    USE - The transformant of yeast (Schizosaccharomyces) is useful for producing modified beta -glucosidase which is useful for decomposing cellulose (all claimed) for producing biofuel.    ADVANTAGE - The beta -glucosidase has thermal stability or glucose inhibition tolerance which is higher than beta -glucosidase derived from filamentous fungi which does not have mutation.    DETAILED DESCRIPTION - A transformant of yeast (Schizosaccharomyces) comprising promoter sequence and terminator sequence for making structural gene to express as an extrachromosomal gene in a chromosome, is new. The structural gene sequence includes a region which encodes modified beta -glucosidase. The beta -glucosidase has thermal stability or glucose inhibition tolerance. The modified beta -glucosidase is derived from filamentous fungi (Aspergillus aculeatus), where the beta -glucosidase has at least one mutation chosen from (a) mutation-1, in which amino acid residue at position 244 (isoleucine) is substituted by phenylalanine, (b) mutation-2, in which amino acid residue at position 282 (glycine) is substituted by phenylalanine, (c) mutation-3, in which amino acid residue at position 442 (asparagine) is substituted by serine, (d) mutation-4, in which amino acid residue at position 452 (glycine) is substituted by serine, (e) mutation-5, in which amino acid residue at position 452 (valine) is substituted by alanine, and (f) mutation-5, in which amino acid residue at position 613 (arginine) is substituted by leucine. INDEPENDENT CLAIMS are included for the following: (1) method for producing the transformant of yeast (Schizosaccharomyces); (2) method for producing modified beta -glucosidase, involves culturing the transformant, obtaining the beta -glucosidase from the microbial cell, and mutating the beta -glucosidase; and (3) method for decomposing cellulose, involves using modified beta -glucosidase obtained by the above-mentioned method.