Cloning and characterization of Arabidopsis thaliana AtNAP57 - a homologueof yeast pseudouridine synthase Cbf5p

Rat Nap57 and its yeast homologue Cbf5p are pseudouridine synthases involve d in rRNA biogenesis, localized in the nucleolus. These proteins, together with H/ACA class of snoRNAs compose snoRNP particles, in which snoRNA guide s the synthase to direct site-specific pseudouridylation of rRNA. In this p aper we present an Arabidopsis thaliana protein that is highly homologous t o Cbf5p (72% identity and 85% homology) and NAP57 (67% identity and 81% hom ology). Moreover, the plant protein has conserved structural motifs that ar e characteristic features of pseudouridine synthases of the TruB class. We have named the cloned and characterized protein AtNAP57 (Arabidopsis thalia na homologue of NAP57). AtNAP57 is a 565 amino-acid protein and its calcula ted molecular mass is 63 kDa. The protein is encoded by a single copy gene located on chromosome 3 of the A. thaliana genome. Interestingly, the AtNAP 57 gene does not contain any introns. Mutations in the human DKC1 gene enco ding dyskerin (human homologue of yeast Cbf5p and rat NAP57) cause dyskerat osis congenita a rare inherited bone marrow failure syndrome characterized by abnormal skin pigmentation, nail dystrophy and mucosal leukoplakia.