The significance of the US3-UL34 catalytic relationship to virus replication is cell type dependent. Replicate cultures of HEp-2 cells (A and B) or Vero cells (C and D) were infected an at MOI of 5 with HSV-1(F) (A to D), vRR1202 (A to D), vRR1202rep (A and C), vRR1204 #1 (A and C), vRR1204 #2 (A and C), vRR1205 #1 (B and D), or vRR1205 #2 (B and D). Residual virus was removed or inactivated with a low-pH wash, and at the indicated times total culture virus was titrated on 143/1099E cells. Virus yields are expressed as PFU per milliliter. Each datum point represents the mean of three experiments. Error bars indicate the sample standard deviations. For ease of comparison with recombinant viruses, the growth data presented in panels A and C for HSV-1(F) and vRR1202 are duplicated in panels B and D.