The tau protein has transposase endonuclease and restriction endonuclease domains, with active regions at the N-terminus, C-terminus, and middle part (Table ). The transposase endonuclease function is exclusively applicable to tau protein's transposase function. The HNH Cas9 enzyme function is the primary application of the restriction endonuclease. (6) Ribonuclease domains EndoU (PS51959) Eukaryotic uridylate-specific endoribonuclease. EndoU is a family of metal-dependent endoribonucleases that are highly conserved in eukaryotes. People in the EndoU family are thought to be involved in many biological processes, including building the endoplasmic reticulum (ER) network, the immune response, neurodegeneration, and the production of small nucleolar RNA. They also possess endoribonuclease and RNA binding activities. The EndoU domain releases the 2',3'-cyclic phosphodiester terminus by cleaving RNA at the uridylate.