The yeast Saccharomyces cerevisiae is a very important unicellular eukaryotic organism that is used as a microbial chassis for the production of biologically active products since the 1980s. It is a robust and genetically well characterized organism that is capable of certain post – translational modifications, such as removal of signal sequence from protein, glycosylation of protein, disulfide bond formation and proper protein folding. However, it also have some disadvantages, such as hyperglycosylation of proteins, which affects the pharmacokinetic properties of biologically active product. Also a challange is the limited secretion of complex proteins and the Crabtree effect and accumulation of ethanol. Various vectors, such as centromeric plasmids, episomal plasmids and integrative vectors are used to indroduce heterologous genes into S. cerevisiae. Plasmids carry marker systems for selection. The most common are auxotrophic markers, autoselection system or dominant markers. Regulatory sequences of promoter and terminator are important for frequency of expression and the stability of the transcript. One of the latest methods for modifying the genome is CRISPR/Cas technology. The best-known examples of biologically active products obtained from S. cerevisiae are hormones, the best example is insulin, various vaccines, blood factors such as hirudin, cytokines and enzymes.
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