ENDOU encodes an endoribonuclease that specifically cleaves single-stranded RNAs at the 5' position of uridylates, producing products with 2',3'-cyclic phosphates at the 3'-end 1. The enzyme shows preferential cleavage at UU and GU sites compared to CU and AU sites 1. ENDOU functions as a post-transcriptional regulator by targeting mRNAs to control their expression 2. During endoplasmic reticulum stress, ENDOU-1 overcomes inhibitory upstream open reading frames in the CHOP transcript's 5'-untranslated region, enabling downstream CHOP translation 3. The enzyme's expression is upregulated during stress conditions through activator elements in its promoter region (-1350 to -1250 nucleotides upstream) 3. In Drosophila studies, the ENDOU ortholog CG2145 was identified as a muscle-secreted protein that binds directly to muscles and promotes activity 4. Clinically, ENDOU expression patterns may serve as a diagnostic biomarker for cervical squamous cell carcinoma, showing decreased expression in tumor tissues compared to normal tissues 5. The protein's endoribonuclease activity positions it as an important regulator of RNA metabolism and cellular stress responses.