Methods for the transfer of molecular substances into eukaryotic cells, mainly for gene transfer, have an enormous impact on biotechnology and medicine. However, there is still a significant demand for non-toxic, efficient, and cheap vector systems; vehicles produced in recombinant Escherichia coli are very attractive in this respect. The Ph.D. thesis presented here is a comparative study on two vector systems based on proteins. One of these vectors uses the main coat protein VP1 from Polyomavirus (PyVP1), the other system is based on the hyperthermophilic protein HU from Thermotoga maritima (TmHU). For the first time recombinantly produced VP1 was shown to transport plasmid DNA into eukaryotic cells. However, the efficiency was low in these experiments. Using N-terminally modified variants of PyVP1 did not improve the transfection yields. The directed packaging of substances in protein shells using matrix immobilization was demonstrated in this work for the first time. The hyperthermophilic protein TmHU was cloned, purified, and analyzed in detail using physicochemical and biochemical methods (e.g. with respect to DNA binding, thermal stability of the protein and TmHU/DNA complexes, respectively). Next, an efficient protocol was developed for the transfection of eukaryotic cells using TmHU. Transfection was successful using several different cell lines. Also, TmHU can be used as an enhancer for lipofection. It was demonstrated that TmHU is useful as a protein transduction domain for proteins and peptides. The protein was tested in vitro (cell culture) as well as in vivo; using mouse models, it was shown that the non-toxic TmHU can improve transfection yields significantly.