PromoFectin provides highly effective and reliable delivery of nucleic acids into a variety of cell types, including many hard-to-transfect cell lines and primary cells such as human endothelial cells, fibroblasts and hepatocytes. It consists of a proprietary non-liposomal, cationic polymer that is stable, water-soluble and free of any components of animal origin. In contrast to many liposome-based transfection reagents, it shows very low toxicity and is therefore ideally suited even for transfection of very sensitive cells yielding optimal transfection efficiencies and gene expression. Transfection with PromoFectin typically requires no medium change and it can be used for highly effective delivery of plasmid DNA as well as oligonucleotides and siRNA into adherent and non-adherent cells. It compacts DNA into positively-charged, stable and protective complexes which bind to negatively-loaded cell-surface residues and enter the cell by endocytosis. In the endosome, PromoFectin acts as a “proton sponge”, buffering the endosomal pH that leads to pH inhibition of endosomal nucleases and ensures stability of the complexes. Continuous proton influx leads to osmotic swelling and rupture of the endosome, allowing a very rapid and almost complete release of the nucleic acids into the cytosol. Moreover, PromoFectin also favors DNA trafficking to the cell nucleus – a property that is particularly useful for transfection of slow-dividing or resting cells.