ABSTRACT
Chromosomal integration enables stable phenotype and therefore has become an important strategy for breeding of industrial Saccharomyces cerevisiae strains. pAUR135 is a plasmid that enables recycling use of antibiotic selection marker, and once attached with designated homologous sequences, integration vector for stable expression can be constructed. Development of S. cerevisiae strains by metabolic engineering normally demands overexpression of multiple genes, and employing pAUR135 plasmid, it is possible to construct S. cerevisiae strains by combinational integration of multiple genes in multiple sites, which results in different ratios of expressions of these genes. Xylose utilization pathway was taken as an example, with three pAUR135-based plasmids carrying three xylose assimilation genes constructed in this study. The three genes were sequentially integrated on the chromosome of S. cerevisiae by combinational integration. Xylose utilization rate was improved 24.4%-35.5% in the combinational integration strain comparing with that of the control strain with all the three genes integrated in one location. Strain improvement achieved by combinational integration is a novel method to manipulate multiple genes for genetic engineering of S. cerevisiae, and the recombinant strains are free of foreign sequences and selection markers. In addition, stable phenotype can be maintained, which is important for breeding of industrial strains. Therefore, combinational integration employing pAUR135 is a novel method for metabolic engineering of industrial S. cerevisiae strains.