VapC-like PIN domain of rRNA-processing protein, Utp23 (YOR004W), and other fungal homologs.
Saccharomyces cerevisiae Utp23 (U three-associated protein 23), component of the small subunit (SSU) processome, is an essential protein involved in pre-rRNA processing and 40S ribosomal subunit assembly. The PIN (PilT N terminus) domain belongs to a large nuclease superfamily. The structural properties of the PIN domain indicate its active center, consisting of three highly conserved catalytic residues which coordinate metal ions, in some members, additional metal coordinating residues can be found. Some members of the superfamily, including S. cerevisiae Utp23, lack several of these key catalytic residues. Mutation of the remaining conserved putative active site residues seen in Utp23 did not interfere with rRNA maturation and cell viability. The PIN active site is geometrically similar in the active center of structure-specific 5' nucleases, PIN-domain ribonucleases of eukaryotic rRNA editing proteins, and bacterial toxins of toxin-antitoxin (TA) operons.
Comment:Utp23 lacks several of the conserved acidic residues found in the active site and mutation of the conserved acidic residues seen in Utp23 did not interfere with rRNA maturation and cell viability.
Jiyao W et al.(2023). "The conserved domain database in 2023.",