ATF4 and Salmonella Infections: Our results suggest that from as early as post 2 h of Salmonella infection, both the transcription factors, ATF4 and ATF6, from the cytosol translocated to the nucleus of infected cells compared with uninfected cells and STMΔssaV infected cells, suggesting that only wild-type Salmonella can activate UPR (Fig. 1A through D).