Various rational metabolic engineering and random approaches have been applied to introduce and improve xylose utilization and ethanol productivity bySaccharomyces cerevisiae. Among them, theBUD21gene was identified as an interesting candidate for enhancing xylose consumption as its deletion appeared to be sufficient to improve growth, substrate utilization and ethanol productivity on xylose, even in a laboratory strain lacking a heterologous xylose pathway. The present study aimed at studying the influence ofBUD21deletion in recombinant strains carrying heterologous oxido-reductive xylose utilization pathway. The positive effect ofBUD21gene deletion on aerobic growth and xylose utilization could not be confirmed in two non-engineered laboratory strains (BY4741 and CEN.PK 113-7D) that were grown in YP rich medium with 20 g/L xylose as sole carbon source, despite the fact that effective deletion ofBUD21gene was confirmed using both genotypic (colony PCR) and phenotypic (heat sensitive phenotype of theBUD21deletion mutant) control experiments. Therefore, the effect ofBUD21deletion on xylose fermentation might be strain- or medium-dependent.