Endoribonuclease that cleaves single-stranded RNAs at 5' of uridylates and releases a product with a 2',3'-cyclic phosphate at the 3'-end. The UU and GU sites are more efficiently cleaved than CU and AU sites. ribonucleotidyl-uridine-RNA = a 3'-end 2',3'-cyclophospho-ribonucleotide-RNA + a 5'-end dephospho-uridine-RNA Monomer. Specifically expressed in T-cells during apoptosis. Expressed in surface heat stable antigen (HSA)-containing T-cells populations (CD4(-)CD8(-)HSA(+), CD4(+)CD8(-)HSA(+), CD4(-)CD8(+)HSA(+), and CD4(+)CD8(+)HSA(+)) and not in the HSA(-) single positive T-cell populations of the thymus or spleen, suggesting that expression is lost during T-cell maturation and is absent at the most mature stages of T-cell development. Belongs to the ENDOU family.