Yeast cells allow high-level expression and formation of polyomavirus-likeparticles

Polyomavirus-derived virus-like particles (VLPs) have been described as pot ential carriers for encapsidation of nucleic acids in gene therapy. Althoug h VLPs can be generated in E. coli or insect cells, the yeast expression sy stem should be advantageous as it is well established for the biotechnologi cal generation of products for human use, especially because they are free of toxins hazardous for humans. We selected the yeast Saccharomyces cerevis iae for expression of the major capsid protein VP1 of a non-human polyomavi rus, the hamster polyomavirus (HaPV). Two entire HaPV VP1-coding sequences, starting with the authentic and a second upstream ATG, respectively, were subcloned and expressed to high levels in Saccharomyces cerevisiae. The exp ressed VP1 assembled spontaneously into VLPs with a structure resembling th at of the native HaPV capsid. Determination of the subcellular localization revealed a nuclear localization of some particles formed by the N-terminal ly extended VP1, whereas particles formed by the authentic VP1 were found m ainly in the cytoplasmic compartment.