Expression of cellulase and xylanase genes. Strains were cultured in medium containing 50 g/L of cellulose for 24 h (A), 72 h (B), 120 h (C), or in 10 g/L of glucose and 40 g/L of cellulose for 48 h (D). Expression levels are shown relative to that of gpdA as an internal control. Black bars, YDCre; white bars, YPyrF. Data are presented as the mean of three experiments.