Published online 13 May 2005
Article |
Unusual features of fibrillarin cDNA and gene structure in Euglena gracilis: evolutionary conservation of core proteins and structural predictions for methylation-guide box C/D snoRNPs throughout the domain Eucarya
Department of Biochemistry and Molecular Biology, Dalhousie University Halifax, Nova Scotia, Canada B3H 1X5
*To whom correspondence should be addressed. Tel: +1 902 494 7035; Fax: +1 902 494 1355; Email: russella{at}dal.ca
Received March 21, 2005. Revised April 25, 2005. Accepted April 25, 2005.
Box C/D ribonucleoprotein (RNP) particles mediate O2'-methylation of rRNA and other cellular RNA species. In higher eukaryotic taxa, these RNPs are more complex than their archaeal counterparts, containing four core protein components (Snu13p, Nop56p, Nop58p and fibrillarin) compared with three in Archaea. This increase in complexity raises questions about the evolutionary emergence of the eukaryote-specific proteins and structural conservation in these RNPs throughout the eukaryotic domain. In protists, the primarily unicellular organisms comprising the bulk of eukaryotic diversity, the protein composition of box C/D RNPs has not yet been extensively explored. This study describes the complete gene, cDNA and protein sequences of the fibrillarin homolog from the protozoon Euglena gracilis, the first such information to be obtained for a nucleolus-localized protein in this organism. The E.gracilis fibrillarin gene contains a mixture of intron types exhibiting markedly different sizes. In contrast to most other E.gracilis mRNAs characterized to date, the fibrillarin mRNA lacks a spliced leader (SL) sequence. The predicted fibrillarin protein sequence itself is unusual in that it contains a glycine-lysine (GK)-rich domain at its N-terminus rather than the glycine-arginine-rich (GAR) domain found in most other eukaryotic fibrillarins. In an evolutionarily diverse collection of protists that includes E.gracilis, we have also identified putative homologs of the other core protein components of box C/D RNPs, thereby providing evidence that the protein composition seen in the higher eukaryotic complexes was established very early in eukaryotic cell evolution.
Present address: Yoh-ichi Watanabe, Department of Biomedical Chemistry, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
The authors wish it to be known that, in their opinion, the first two authors should be regarded as joint First Authors
DDBJ/EMBL/GenBank accession nos+