FIGURE 8.

NS4B is capable of focus formation, but the NS4B5A precursor is not. A, GFP-tagged NS4B, NS5A, and NS4B5A were expressed in Huh7.5 cells using recombinant baculovirus transduction and visualized by confocal microscopy. For NS4B-GFP, the GFP tag was inserted at the COOH terminus of the protein; for the other constructs, it was inserted at a position within domain 3 of NS5A capable of tolerating insertion without loss of NS5A replicative function. Cell nuclei are shown counterstained red. B, a proposed model for the role of the NS4B5A precursor in regulating NS4B-induced curvature of the membrane to form the replication complex. In this model, cleavage of the NS4B5A boundary is required to go to completion for maturation of the replication complex. Slow cleavage allows for efficient recruitment of host cell proteins.