Characterization of a Nove1 ArginineEerine-Rich Splicing Factor in Arabidopsis

Many splicing factors in vertebrate nuclei belong to a class of evolutionarily conserved proteins containing argininekerine (RS) or serine/arginine (SR) domains. Previously, we demonstrated the existence of SR splicing factors in plants. In this article, we report on a nove1 member of this splicing factor family from Arabidopsis designated atRSp31. It has one N-terminal RNA recognition motif and a C-terminal RS domain highly enriched in arginines. The RNA recognition motif shows significant homology to all animal SR proteins identified to date, but the intermediate region does not show any homology to any other known protein. Subsequently, we characterized two cDNAs from Arabidopsis that are highly homologous to atRSp3l (designated atRSp35 and atRSp41). Their deduced amino acid sequences indicate that these proteins constitute a new family of RS domain splicing factors. Purified recombinant atRSp3l is able to restore splicing in SR protein-deficient human SlOO extracts. This indicates that atRSp3l is a true plant splicing factor and plays a crucial role in splicing, similar to that of other RS splicing factors. All of the three genes are differentially expressed in a tissuespecific manner. The isolation of this new plant splicing factor family enlarges the essential group of RS domain splicing factors. Furthermore, because no animal equivalent to this protein family has been identified to date, our results suggest that these proteins play key roles in constitutive and alternative splicing in plants.