Archaeal Cbf5 is the catalytic subunit of H/ACA small nucleolar ribonucleoprotein (H/ACA box snoRNP) complex. It catalyzes the pseudouridylation of rRNA, snRNA and also intron-containing pre-tRNA. It works with 3 other subunits, Gar1, Nop10 (two homologs of eukaryotic Gar1p/Nop10p), and ribosomal protein L7Ae that is unique to Archaea. However, only Nop10 seems important for tRNA modification. Archaeal L7Ae is the only core protein that is also shared by the C/D box snoRNP. Comparison of archaeal Cbf5 with bacterial tRNA Psi55 synthase (TruB) reveals structural conservation and provides insight into the guide-independent activity of archaeal Cbf5.