Virus-like gene transfer into cells mediated by polyoma virus pseudocapsids

Mouse polyoma virus-like particles (or pseudocapsids) are composed solely o f recombinant viral coat protein. They can interact with DNA and transport it to cells, resulting in gene expression both in tissue culture and in mic e. We demonstrate that DNA transfer in vitro depends on partial packaging o f DNA within the virus-like capsid. Cell surface sialic acid residues and a n intact microtubule network, required for viral infectivity, are also nece ssary for pseudocapsid-mediated gene expression from heterologous DNA. Thus , gene delivery in this system requires pathways utilised by polyoma virion s, rather than proceeding via the 'nonspecific' endosomal route typical of nonviral systems such as liposomes or calcium phosphate precipitates. Despi te the fact that all cells appear to internalise pseudocapsid/DNA complexes , only a proportion show productive gene delivery. Bulk internalisation of complexes is dependent on actin fibres, but not cell surface sialic acid or microtubules, indicating that a second transport pathway exists for pseudo capsids which is nonproductive for gene transfer. The model suggested by th ese data demonstrates the virus-like properties of the pseudocapsid system, and provides a basis for further development to produce a highly effective gene delivery vehicle.