cd09876

PIN domain of eukaryotic ribosome assembly factor Nob1 and archaeal UPF0129 protein Ta0041-like homologs; PIN (PilT N terminus) domain of the Saccharomyces cerevisiae ribosome assembly factor, Nob1 (Nin one binding) protein, the Thermoplasma acidophilum DSM 1728, UPF0129 protein Ta0041, and similar eukaryotic and archaeal homologs are included in this family. The Nob1 PIN domain binds the single-stranded cleavage site D at the 3#end of 18S rRNA. Recombinant Nob1 binds as a tetramer to pre-18S rRNA fragments containing cleavage site D and believed to cleave at this site. These PIN domains are homologs of flap endonuclease-1 (FEN1)-like PIN domains, but lack the extensive arch/clamp region and the H3TH (helix-3-turn-helix) domain, an atypical helix-hairpin-helix-2-like region, seen in FEN1-like PIN domains. PIN domains within this subgroup contain three highly conserved acidic residues (putative metal-binding, active site residues).