A gene fusion encoding a bifunctional protein, protein A-cellulase (PAC), with IgG- and cellulose-binding activities, was constructed by the fusion of a genomic fragment encoding the IgG-binding domains of Staphylococcus aureus protein A and the cellulose-binding domain plus hinge from Phanerochaete chrysosporium exoglucanase CBH 1.1 cDNA. The hybrid protein PAC presents both IgG- and cellulose-binding activities. The properties presented by PAC make it possible to use in an alternative procedure in the purification of IgG molecules. This kind of protein could also be used as a model in the study of mechanisms involved in the adsorption of cellulases to cellulose.