Nat. Cell Biol. 14, 1223–1230 (2012); published online 28th October 2012; corrected online 15th November 2012

While this manuscript was under consideration, an article by Di Paola et al. reported an ER localization for PARP16. In the version of this Letter initially published online and in print, the reference (PLoS ONE 7, e37352; 2012) was inadvertently omitted from the reference list. On page 8, the following text has replaced the previous text:

We show that the ER-associated tail-anchored protein PARP16 selectively ADP-ribosylates PERK and IRE1α during the UPR, and that such modification is required for activation of PERK and IRE1α at least in part by increasing their kinase and endonuclease activities. While this manuscript was under revision, Di Paola et al. independently showed that PARP16 is ER-localised, and a tail-anchored protein22. Interestingly, Saccharomyces cerevisiae lacks PARP proteins and has only one ER stress sensor, Ire1.

The omitted reference has now been added to the reference list:

22. Di Paola, S., Micaroni, M., Di Tullio, G., Buccione, R. & Di Girolamo, M. PARP16/ARTD15 is a novel endoplasmic-reticulum-associated mono-ADP-ribosyltransferase that interacts with, and modifies karyopherin-β1. PLoS ONE 7, e37352 (2012).

References 22–27 have been changed to 23–28, respectively.