Assembly of Herpes Simplex virus Type 1 Capsids Using a Panel of Recombinant Baculoviruses

Abstract

Immature or B capsids of herpes simplex virus type 1 (HSV-1) are composed of seven proteins encoded by six viral genes. The proteins encoded by UL18 (VP23), UL19 (VP5), UL35 (VP26) and UL38 (VP19C) are components of the outer capsid shell whereas those specified by UL26 (VP21 and VP24) and UL26.5 (VP22a), are involved in scaffold formation. We have used a panel of recombinant baculoviruses, each expressing one of the capsid protein genes, to examine the requirements for capsid assembly. Coexpression of the six genes in insect cells resulted in the formation of capsids that were indistinguishable in appearance and protein composition from those made during HSV-1 infection of mammalian cells. This demonstrates that the proteins encoded by the known capsid genes contain all the structural information necessary for capsid assembly and that other virus-encoded proteins are not required for this process. Omission of single recombinant baculoviruses from this system allowed the role of individual HSV-1 proteins in capsid assembly to be determined. Thus, capsid assembly did not take place in the absence ofVP23, VP5 or VP19C, whereas lack of VP26 had no discernible effect on capsid formation. Capsids assembled in the absence of the UL26 gene products had a large-cored phenotype resembling that previously described for the HSV-1 mutant tsl201 which has a lesion in this gene. Some apparently intact capsid shells were also made in the absence of the major scaffolding protein, VP22a, whereas the omission of both UL26 and UL26.5 resulted in the appearance of large numbers of partial and deformed capsid shells.

Multiple Interactions Control the Intracellular Localization of the Herpes Simplex Virus Type 1 Capsid Proteins

“…Fluorescence experiments were done with BHK-21 C13 cells cultured in Glasgow modified Eagle's medium supplemented with 10% tryptose phosphate and 10% new-born calf serum. Recombinant baculoviruses were grown on Spodoptera frugiperda (Sf2I) cells as described previously (Tatman et al,, 1994 …”

“…The most interesting results have come from recombinant baculoviruses expressing all six capsid protein genes to assemble HSV-1 capsids in insect cells (Tatman et al, 1994;Thomsen et aI., 1994). These studies have Author for correspondence: Frazer J.…”

“…In an earlier study we showed that VP5 and VP23 failed to localize efficiently to the nucleus when expressed using vaccinia virus or plasmid based expression systems (Nicholson et al, 1994), thereby demonstrating that neither of these proteins contains a nuclear localization signal. Nuclear localization of VP5 did occur when it was coexpressed with preVP22a.…”

“…Expression plasmids were constructed by cloning the capsid protein genes under the control of the HCMV immediate-early (IE) promoter present in the plasmid pCMV10 (Stow et a/., 1993). The construction of the plasmids, pE18, pE19 and pJK2 expressing VP23, VP5 and preVP22a respectively, has been described previously (Nicholson et al, 1994). The cloning of the UL38 (VPI9C) ORF into pBJ182 was described by Tatman et al (1994).…”

“…Cells were transfected using a lipofection procedure as described previously (Nicholson et al, 1994).…”