Rational engineering of S. cerevisiae expressing a xylose isomerase pathway. Rational strain engineering in a gre3 background containing an integrated copy of xylA 3* and XKS1 overexpression (SXA-R1 strain) was evaluated. In addition, the expression of an additional copy of xylA3* and tal1 overexpression (square), and pho13 deletion (black) gradually improved the cell growth on xylose. Strain identifications (SXA-R1: white circle, SXA-R2: white square, SXA-R1P: black circle, and SXA-R2P: black square) are described in the text. The expression of an additional copy of xylA3* and pho13 deletion showed synergistic effect on the cell growth on xylose. Error bars represent the standard deviation of biological triplicates.