cd09864

PIN domain of rRNA-processing protein, Fcf1 (Utp24, YDR339C), and other eukaryotic homologs; Fcf1/Utp24 (FAF1-copurifying factor 1/U three-associated protein 24) is an essential protein involved in pre-rRNA processing and 40S ribosomal subunit assembly. Component of the small subunit (SSU) processome, Fcf1 is an essential nucleolar protein that is required for processing of the 18S pre-rRNA at sites A0-A2. The Fcf1 protein was reported to interact with Pmc1p (vacuolar Ca2+ ATPase) and Cor1p (core subunit of the ubiquinol-cytochrome c reductase complex). The PIN (PilT N terminus) domain of this protein is a homolog of flap endonuclease-1 (FEN1)-like PIN domains, but apparently lack the H3TH domain or extensive arch/clamp region seen in the latter. PIN domains typically contain three or four conserved acidic residues (putative metal-binding, active site residues). The Fcf1 PIN domain subfamily has four of these putative active site residues and the Fcf1-Utp23 homolog PIN domain subfamily has three of them. Point mutation studies of the conserved acidic residues in the putative active site of Saccharomyces cerevisiae Fcf1 determined they were essential for pre-rRNA processing at sites A1 and A2, whereas the presence of the Fcf1 protein itself is also required for cleavage at site A0.