Indicate whether each of the following descriptions better matches the ATF6 (A), the IRE1 (I), or the PERK (P) branch of the ER unfolded protein response. Your answer would be a four-letter string composed of letters A, I, and P only, e.g. APII.
( ) It involves a noncanonical cytoplasmic splicing process.
( ) Its sensor is a latent transcription regulator.
( ) It involves regulated proteolysis of the sensor protein in the Golgi apparatus.
( ) Its sensor bears both kinase and endoribonuclease activities.