title: Computational identification of four spliceosomal snRNAs from the deep-branching eukaryote Giardia intestinalis.
abstract: RNAs processing other RNAs is very general in eukaryotes, but is not clear to what extent it is ancestral to eukaryotes. Here we focus on pre-mRNA splicing, one of the most important RNA-processing mechanisms in eukaryotes. In most eukaryotes splicing is predominantly catalysed by the major spliceosome complex, which consists of five uridine-rich small nuclear RNAs (U-snRNAs) and over 200 proteins in humans. Three major spliceosomal introns have been found experimentally in Giardia; one Giardia U-snRNA (U5) and a number of spliceosomal proteins have also been identified. However, because of the low sequence similarity between the Giardia ncRNAs and those of other eukaryotes, the other U-snRNAs of Giardia had not been found. Using two computational methods, candidates for Giardia U1, U2, U4 and U6 snRNAs were identified in this study and shown by RT-PCR to be expressed. We found that identifying a U2 candidate helped identify U6 and U4 based on interactions between them. Secondary structural modelling of the Giardia U-snRNA candidates revealed typical features of eukaryotic U-snRNAs. We demonstrate a successful approach to combine computational and experimental methods to identify expected ncRNAs in a highly divergent protist genome. Our findings reinforce the conclusion that spliceosomal small-nuclear RNAs existed in the last common ancestor of eukaryotes.
authors.affiliation: Allan Wilson Centre for Molecular Ecology and Evolution, IMBS, Massey University, Palmerston North, New Zealand. sylvia.x.chen@gmail.com
authors.forename: Xiaowei Sylvia
authors.initials: XS
authors.lastname: Chen
authors.forename: W Timothy J
authors.initials: WT
authors.lastname: White
authors.forename: Lesley J
authors.initials: LJ
authors.lastname: Collins
authors.forename: David
authors.initials: D
authors.lastname: Penny