As a step to breed a Saccharomyces cerevisiae strain able to produce ethanol directly from cellulose, we combined cDNA for Aspergillus aculeatus FI-CMCase (FI-carboxymethyl cellulase) with the GAP (glyceraldehyde-3-phosphate dehydrogenase) promoter of S. cerevisiae and used the resultant plasmid, pYEC91, to transform S. cerevisiae. The transformed cells produced active FI-CMCase within the cytoplasm. Western-blot analysis following SDS-polyacrylamide gel electrophoresis demonstrated that the cells contained a peptide having the same molecular mass and immunological identity as A. aculeatus FI-CMCase.