Domain within Herpes Simplex Virus 1 Scaffold Proteins Required for Interaction with Portal Protein in Infected Cells and Incorporation of the Portal Vertex into Capsids

The portal vertex of herpesvirus capsids serves as the conduit through which DNA is inserted during the assembly process. In herpes simplex virus (HSV), the portal is composed of 12 copies of the UL 6 gene product, pUL 6. Previous results identified a domain in the major capsid scaffold protein, ICP35, required for interaction with pUL 6 and its incorporation into capsids formed in vitro (G. P. Singer et al., J. Virol. 74:6838-6848, 2005). In the current studies, pUL 6 and scaffold proteins were found to coimmunoprecipitate from lysates of both HSV-infected cells and mammalian cells expressing scaffold proteins and pUL 6. The coimmunoprecipitation of pUL 6 and scaffold proteins was precluded upon deletion of codons 143 to 151 within UL 26.5, encoding ICP35. While wild-type scaffold proteins colocalized with pUL 6 when transiently coexpressed as viewed by indirect immunofluorescence, deletion of UL 26.5 codons 143 to 151 precluded this colocalization. A recombinant herpes simplex virus, vJB11, was generated that lacked UL 26.5 codons 143 to 151. A virus derived from this mutant but bearing a restored UL 26.5 was also generated. vJB11 was unable to cleave or package viral DNA, whereas the restored virus packaged DNA normally. vJB11 produced ample numbers of B capsids in infected cells, but these lacked normal levels of pUL 6. The deletion in UL 26.5 also rendered pUL 6 resistant to detergent extraction from vJB11-infected cells. These data indicate that, as was observed in vitro, amino acids 143 to 151 of ICP35 are critical for (i) interaction between scaffold proteins and pUL 6 and (ii) incorporation of the HSV portal into capsids.