A1.

Group 5 has designed several vector systems for very efficient transient expression of proteins in mammalian cell culture (6). Development of the system using regulatory elements from DNA viruses is continuing in close collaboration with the Estonian biotech company Icosagen. Another system being developed concerns the design of RNA viruses genomes that produce recombinant proteins either in a transient manner or by generating specific cell lines for long term expression (7). These systems can be used separately or, if needed, combined with each other. The main benefit of production of mammalian proteins in mammalian cells is the retention of the native posttranslational modification patterns (8). Still, several complications can arise in practical production settings (8, 9). For example, the immortalized cell lines might produce different modification patterns as compared to the tissues where the biomolecule is natively produced. In addition, during protein overexpression the activities of the modification enzymes are often not high enough leading to incompletely modified, heterogeneous products. We will engineer the modification pathways by overexpressing and/or inactivating the set of genes encoding for proteins responsible for key steps in the pathways. This is expected to lead to homogenous products with the desired modification patterns. As a next step, attempts will be made to engineer protein production cell lines where new posttranslational modification patterns could be produced in a controlled manner.

Cell engineering will be performed by group 5 and product characterization by group 2 (proteomics).