INDUCED EXTRUSION OF DNA FROM THE CAPSID OF HERPES-SIMPLEX VIRUS TYPE-1

DNA-filled capsids (C capsids) of herpes simplex virus type 1 were tre ated in vitro with guanidine-HCl (GuHCl) and analyzed for DNA loss by sucrose density gradient ultracentrifugation and electron microscopy. DNA was found to be lost quantitatively from virtually all capsids tre ated with GuHCl at concentrations of 0.5 M or higher, while 0.1 M GuHC l had little or no effect. DNA removal from 0.5 M GuHCl-treated capsid s was effected without significant change in the capsid protein compos ition, as judged by sodium dodecyl sulfate-polyacrylamide gel electrop horesis, or in its structure, as judged by electron microscopy. Electr on microscopic examination of capsids in the process of emptying showe d that DNA was extruded from multiple, discrete sites which appeared t o coincide with capsid vertices. DNA exited the capsid in the form of thick strands or fibers that varied in diameter from approximately 4 t o 13 nm with preferred diameters of 7 and 11 nm. The fibers most proba bly correspond to multiple, laterally aligned DNA segments, as their d iameters are nearly all greater than that of a single DNA double helix . The results suggest that GuHCl treatment promotes an alteration in t he capsid pentons which allows DNA to escape locally. Herons must be m ore resistant to this change, since DNA loss appears to be restricted to the pentons. The ability of GuHCl to cause loss of DNA from C capsi ds with no accompanying change in capsid morphology or protein composi tion suggests that penton sites may open transiently to permit DNA exi t and then return to their original state.