CAPSID ASSEMBLY AND DNA PACKAGING IN HERPES-SIMPLEX VIRUS

The genome of HSV-1 contains 80-85 open reading frames. Genetic and bi ochemical evidence suggests that at least 39 of these genes encode pro teins that are components of the HSV-1 virion. The architecture of the HSV-1 virion consists of a trilaminar lipid envelope, an amorphous la yer known as the tegument, a capsid shell, and a DNA-containing core. The capsid is an icosahedral shelf whose major morphological features are 162 capsomers. It is composed of a major capsid protein called VP5 and three less abundant proteins, VP19C, VP23 and VP26. VP5 is the st ructural subunit of all 162 capsomers while VP19C and VP23 are located in the space between the capsomers. In addition to the structural pro teins, capsid assembly involves participation of the HSV-1-encoded pro tease and the scaffolding protein, preVP22a. DNA packaging involves pa rticipation of DNA, empty capsids, and at least seven additional HSV-1 -encoded proteins. Considerable advances have been made in understandi ng the structure of the capsid shell, largely as the result of applyin g cryoelectron microscopy techniques. Use of recombinant baculoviruses has allowed for a detailed analysis of the proteins required for caps id assembly. More recently, an in vitro system has been developed whic h has aided in defining the assembly pathway by identifying intermedia tes in the assembly of intact capsids. The in nitro system has identif ied a fragile roundish procapsid which matures into the polyhedral cap sid in a transition similar to that undergone by bacteriophage prohead s. This review is a summary of our present knowledge with respect to t he structure and assembly of the HSV-1 capsid and what is known about the seven genes involved in DNA packaging. (C) 1997 by John Wiley & So ns Ltd.