Polyoma-like particle: characterization of the DNA encapsidated in vitro by polyoma empty capsids.

Polyoma empty capsids and DNA interact in a cell-free system to form a polyoma-like particle (PLP). The particle is stable in high concentrations of salt and contains a DNA fragment that is protected by the capsid from the action of DNase I. The DNA extracted from PLP is heterogeneous in size. It has a mean molecular weight of 1.2 x 10(6) with a standard deviation of +/- 0.5 x 10(6). Analysis of PLP DNA with restriction endonucleases and the Southern blot technique reveals that a specific primary sequence is not required for PLP formation. Either linear, circular, or supercoiled polyoma DNA, as well as single-stranded DNA, rRNA, and the synthetic homopolymers poly(dA) . poly(dT) and poly(dG) . poly(dC) can be used for PLP formation. It is concluded that polyoma empty capsids can be used to bind and encapsidate nucleic acids differing in their primary, secondary, and superhelical tertiary structure to form, in vitro, stable polyoma-like particles.