Effect of NS4B carboxy terminal mutations on colony formation using selectable replicons. Colony formation assay in which Huh7 cells are transfected with in vitro transcribed replicon RNA that contain NS4B-CTD mutations. Colonies were stained using Coomassie blue. Wild-type is pFK5.1. Mock transfected cells as the control. The NS4B-CTD mutations TripleE, E247, E248 and helix-swop in pFK5.1 are explained in figure 4.