RPS3 and infection: US3a and US3b, two isoforms of PRV US3, both upregulate anti-apoptotic signalling through transient overexpression, but the anti-apoptosis effect of US3a is greater than that of US3b. Similar to HSV-1 US3, the kinase activity of PRV US3 is indispensable for its anti-apoptotic activity.129 In the presence of US3, phosphorylated IκBα increases in the early stage of infection to suppress apoptosis.