Interactions of heterologous DNA with polyomavirus major structural protein, VP1

`Empty' polyomavirus pseudocapsids, self-assembled from the major structural protein VP1, bind DNA non-specifically and can deliver it into the nuclei of mammalian cells for expression [Forstová et al. (1995) Hum. Gene Ther. 6, 297–306]. Formation of suitable VP1-DNA complexes appears to be the limiting step in this route of gene delivery. Here, the character of VP1-DNA interactions has been studied in detail. Electron microscopy revealed that VP1 pseudocapsids can create in vitro at least two types of interactions with double-stranded DNA: (i) highly stable complexes, requiring free DNA ends, where the DNA is partially encapsidated; and, (ii) weaker interactions of pseudocapsids with internal parts of the DNA chain.