Successful exogenous transport and metabolic pathways introduced in S. cerevisiae. Reported improvements of pentose utilization in yeast (as described in the text) are depicted in this schematic. (A) Bacterial xylose isomerase pathway; (B) fungal xylose oxidoreductase pathway; (C) Fungal arabinose oxidoreductase pathway; (D) Bacterial arabinose isomerase pathway. The genes used to accomplish the enzymatic step are italicized. Heterologous steps are indicated by dashed lines.