Evolution of intron/exon structure of DEAD helicase family genes in Arabidopsis, Caenorhabditis, and Drosophila

The DEAD box RNA helicase (RH) proteins are homologs involved in diverse ce llular functions in all of the organisms from prokaryotes to eukaryotes. Ne vertheless, there is a lack of conservation in the splicing pattern in the 53 Arabidopsis thaliana (AtRHs), the 32 Caenorhabditis elegans (CeRHs) and the 29 Drosophila melanogaster (DmRHs) genes. Of the 153 different observed intron positions, 4 are conserved between AtRHs, CeRHs, and DmRHs, and one position is also found in RHs from yeast and human. Of the 27 different At RH structures with introns, 20 have at least one predicted ancient intron i n the regions coding for the catalytic domain. In all of the organisms exam ined, we found at least one gene with most of its intron predicted to be an cient. In A, thaliana, the large diversity in RH structures suggests that d uplications of the ancestral RH were followed by a high number of intron de letions and additions. The very high bias toward phase 0 introns is in favo r of intron addition, preferentially in phase 0. Results from this comparat ive study of the same gene family in a plant and in two animals are discuss ed in terms of the general mechanisms of gene family evolution.