VapC-like PIN domain of rRNA-processing protein Fcf1- and Utp23-like homologs found in eukaryotes except fungi; similar to human rRNA-processing protein UTP23
PIN domain homologs of Fcf1/Utp24 (FAF1-copurifying factor 1/U three-associated protein 24) and Utp23, essential proteins involved in pre-rRNA processing and 40S ribosomal subunit assembly, are included in this subfamily. It includes human UTP24 which hUTP24 plays a crucial role in human rRNA processing and is essential for accurate endonucleolytic cleavage at the 5'-end of 18S rRNA. Fcf1 is a component of the small subunit (SSU) processome and an essential nucleolar protein required for processing of the 18S pre-rRNA at sites A0-A2. 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 while some others lack several of these key catalytic residues. The Fcf1-Utp23 homolog PIN domain subfamily has three of these conserved acidic residues rather than the four seen in the Fcf1 PIN domain subfamily.
Comment:Point mutation studies showed that the conserved acidic residues in the putative active site of Saccharomyces cerevisiae Fcf1 are essential for 18S pre-rRNA processing at sites A1 and A2.
Comment:The Fcf1 PIN domain subfamily has four of these putative active site residues and the Fcf1-Utp23 homology PIN domain subfamily has three of them.
Comment:Utp23 lacks several of these conserved acidic residues 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.",