Upstream Activation Sequence Can Function as an Insulator for Chromosomal Regulation of Heterologous Pathways Against Position Effects in Saccharomyces cerevisiae.

Metabolic engineering of microbial cell factories through integrating the heterologous synthetic pathway into the chromosome is most commonly used for industrial applications. However, the position of the foreign gene in the chromosome can affect its transcriptional level. As a microorganism that is generally regarded as safe (GRAS) and commonly applied in industrial manufacture with large-scale operations, Saccharomyces cerevisiae is also confronted with this position effect. In this study, we characterized 12 different chromosome sites by inserting the lycopene biosynthetic pathway as a reporter cassette. Due to the different integration loci, the gene transcription and lycopene yield exhibited more than 58-fold and 3.8-fold differences, respectively. Furthermore, changing the gene order also revealed a remarkable influence (30-fold and 14-fold) on gene transcription and lycopene yield. Besides, the upstream activation sequence of a strong promoter (defined as an insulator) in S. cerevisiae could reduce the impact by gene order, and increased the gene transcription (tenfold) and lycopene yield (sevenfold). Taken together, our results demonstrated that gene order and insulator affected gene transcription and heterogeneous biosynthesis, opening the opportunity to regulate gene transcription by insulator against position effect in S. cerevisiae.