Comparative growth analysis of yeast cells expressing the xtrD transporter gene. (A) Subcellular localization of XtrD::GFP in S. cerevisiae when incubated in glucose-rich media, as determined by fluorescent microscopy (scale bar, 5 μm). (B) Growth of strain EBY.VW4000 containing the xtrD gene (+ xtrD) or harboring the empty expression vector (- xtrD) but containing the xylose reduction pathway. Tenfold dilutions were made and cells were spotted onto agar medium supplemented with the relevant carbon source and incubated at 30°C for 144 h. (C) Comparative growth of two different xtrD-expressing S. cerevisiae strains in the presence of xylose. Cells without xtrD (- xtrD) and cells containing the xtrD gene (+ xtrD) before and after (clone 28) a 21-day xylose adaptation period were diluted and spotted onto agar plates (as described above).