GO:0070055:   obsolete mRNA endonucleolytic cleavage involved in unfolded protein response
OBSOLETE. The endonucleolytic cleavage of a mRNA containing an HAC1-type intron at the 5" and 3" splice sites. The cleavage step is part of unconventional mRNA splicing, and contributes to the endoplasmic reticulum unfolded protein response.