Complementation of a gl-deficient feline herpesvirus recombinant by allotopic expression of truncated gl derivatives

The alphaherpesvirus glycoproteins gE and gl farm a hetero-oligomeric compl ex involved in cell-to-cell transmission. The gl-deficient recombinant feli ne herpesvirus (FHV), FHV Delta gl-LZ, produces plaques that are only 15% t he size of those of wild-type FHV. Here, we have complemented FHV Delta gl- LZ allotopically by expressing intact gl and C-terminally truncated gl deri vatives from the thymidine kinase locus. The effect on gE-gl-mediated cell- to-cell spread was assessed by plaque assay employing computer-assisted ima ge analysis (software available at http://www.androclus.vet.uu.nl/ spotter/ spotter.htm). Allotopic complementation with intact gl fully restored plaqu e size. Deletion of the C-terminal 11 residues of gl did not affect cell-to -cell spread, whereas deletion of the complete cytoplasmic tail reduced pla que size by only 35%. Mutants expressing gl(166), roughly corresponding to the N-terminal half of the ectodomain, displayed a small-plaque phenotype. Nevertheless, their plaques were reproducibly larger than those of matched gl-deficient controls, indicating that the gE-gl(166) hetero-oligomer, thou gh crippled, is still able to mediate cell-to-cell spread. Our data demonst rate that plaque analysis provides a reliable and convenient tool to measur e and quantitate gE-gl function in vitro.