This group consists of eukaryotic pseudouridine synthases similar to Saccharomyces cerevisiae Pus1 and Pus2 []. Pseudouridine synthases catalyze the isomerization of specific uridines in an RNA molecule to pseudouridines (5-ribosyluracil, psi) []. No cofactors are required. S. cerevisiae Pus1 catalyzes the formation of psi34 and psi36 in the intron-containing tRNAIle, psi35 in the intron-containing tRNATyr, psi27 and/or psi28 in several yeast cytoplasmic tRNAs and, psi44 in U2 small nuclear RNA (U2 snRNA) []. The presence of the intron is required for the formation of psi 34, 35 and 36. In addition S. cerevisiae PUS1 makes are psi 26, 65 and 67. C. elegans Pus1 does not modify psi44 in U2 snRNA []. Mouse Pus1 makes psi27/28 in pre- tRNASer , tRNAVal and tRNAIle, psi 34/36 in tRNAIle and, psi 32 and potentially 67 in tRNAVal. Psi44 in U2 snRNA and psi32 in tRNAs are highly phylogenetically conserved. Psi 26,27,28,34,35,36,65 and 67 in tRNAs are less highly conserved. Mouse Pus1p regulates nuclear receptor activity through pseudouridylation of Steroid Receptor RNA Activator []. Missense mutation in human PUS1 causes mitochondrial myopathy and sideroblastic anemia (MLASA) [].
Pseudouridine synthases catalyse the isomerisation of uridine to pseudouridine (Psi) in a variety of RNA molecules, and may function as RNA chaperones. Pseudouridine is the most abundant modified nucleotide found in all cellular RNAs. There are four distinct families of pseudouridine synthases that share no global sequence similarity, but which do share the same fold of their catalytic domain(s) and uracil-binding site and are descended from a common molecular ancestor. The catalytic domain consists of two subdomains, each of which has an α+β structure that has some similarity to the ferredoxin-like fold (note: some pseudouridine synthases contain additional domains). The active site is the most conserved structural region of the superfamily and is located between the two homologous domains. These families are [, ]:Pseudouridine synthase I, TruA.Pseudouridine synthase II, TruB, which contains and additional C-terminal PUA domain.Pseudouridine synthase RsuA. RluB, RluE and RluF are also part of this family.Pseudouridine synthase RluA. TruC, RluC and RluD belong to this family.Pseudouridine synthase TruD, which has a natural circular permutation in the catalytic domain, as well as an insertion of a family-specific α+β subdomain.This entry represents pseudouridine synthase I (TruA) from prokaryotes and tRNA pseudouridine synthase 1 (Pus1) from eukaryotes, which belongs to the TruA family. TruA from Escherichia coli modifies positions uracil-38, U-39 and/or U-40 in tRNA [, ]. TruA contains one atom of zinc essential for its native conformation and tRNA recognition and has a strictly conserved aspartic acid that is likely to be involved in catalysis []. This protein adopts a dimeric assembly and shows two positively charged, RNA-binding clefts along their surface. Each cleft contains a highly conserved aspartic acid located at its centre. The structural domains have a topological similarity to those of other RNA-binding proteins, though the mode of interaction with tRNA appears to be unique. Pus1 from Saccharomyces cerevisiae acts at positions 27 and 28 of tRNAs, at positions 34 and 36 of intron-containing precursor tRNA(Ile), at position 35 in the intron-containing tRNA(Tyr) and at position 44 in U2 snRNA [, , ]. This enzyme also catalyses pseudouridylation of mRNAs [].
