The rational design of expression vectors and genes is being investigated as part of the development of novel active pharmaceutical ingredients and expression systems. The research focuses on regulatory elements of transcription and translation (e.g. promoters and UT regions) as well as on the coding sequences themselves. The aim of the research is the targeted optimization of these genetic elements with regard to the optimal yields of recombinant protein in various expression systems such as plants and mammalian cells, but also cell-free systems. The optimization also takes into account process development requirements and can include the directed modification of amino acids that are relevant for product purification. The expression cassettes are tested in common systems such as Escherichia coli, Saccharomyces cerevisiae, and Chinese Hamster Ovary (CHO) cells, but especially with our PCPs (plant cell packs) and cell-free methods.