Fig. 4.

Translational pausing enables XBP1u-RNC to be a client for the SRP-mediated ER-targeting pathway. (A) Coimmunoprecipitation of FH-XBP1u[WT], FH-XBP1u[S255A], and FH-XBP1u[W256A] with the indicated proteins in the cell lysate derived from HEK293T cells transiently expressing FH-XBP1u[WT] and its variants. FH-XBP1u[S255A] and FH-XBP1u[W256A] are the prolonged- and pausing-defective mutants, respectively. (B) Wild-type and variants of HA-XBP1u[nonsplicing] transiently expressed in Cos-7 cells were costained with endogenous Sec61β. (C and D) FRAP analysis of Venus-XBP1u[WT/nonsplicing] or Venus-XBP1u[W256A/nonsplicing] transiently expressed in Cos-7 cells is shown. (D) Merged image of Venus-XBP1u[WT/nonsplicing] and mCherry-Sec61β (ER marker) at 30 min after photobleaching. The detailed analysis is the same as described in Fig. 1C. (Scale bars, 10 μm.)