Revisiting the function of the HSV-1 UL45 protein

The function of many viral proteins encoded by the open reading frames of herpes simplex virus have been studied and characterized, while others remain obscure. UL45 encodes an 18 kDa (18K) non-glycosylated virion envelope protein that is dispensable for in vitro replication. Previous studies reported that it was a mediator of glycoprotein B cell-cell fusion in infected cells, and that gB driven fusion did not occur in the absence of 18K. Using a HSV-1 strain 17 bacterial artificial chromosome we generated a point mutation that removed the UL45 start site. An HA epitope tag was added to the C-terminus for detection in western blotting. Recombinant viruses containing either glycoprotein B (gB) or glycoprotein K (gK) mutations that confer a syncytial phenotype, and with or without UL45 expression, were generated to revisit the role of 18K in mediating cell fusion. We were unable to reproduce the previously reported phenotype and, using this new set of recombinant viruses, showed that UL45 expression was not required for either gB- or gK-driven syncytial plaque formation.