CHARACTERIZATION OF A NOVEL ARGININE SERINE-RICH SPLICING FACTOR IN ARABIDOPSIS/

Many splicing factors in vertebrate nuclei belong to a class of evolut ionarily conserved proteins containing arginine/serine (RS) or serine/ arginine (SR) domains, Previously, we demonstrated the existence of SR splicing factors in plants. In this article, we report on a novel mem ber of this splicing factor family from Arabidopsis designated atRSp31 . It has one N-terminal RNA recognition motif and a C-terminal RS doma in highly enriched in arginines. The RNA recognition motif shows signi ficant homology to all animal SR proteins identified to date, but the intermediate region does not show any homology to any other known prot ein. Subsequently, we characterized two cDNAs from Arabidopsis that ar e highly homologous to atRSp31 (designated atRSp35 and atRSp41). Their deduced amino acid sequences indicate that these proteins constitute a new family of RS domain splicing factors. Purified recombinant atRSp 31 is able to restore splicing in SR protein-deficient human S100 extr acts. This indicates that atRSp31 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 tis sue-specific manner, The isolation of this new plant splicing factor f amily enlarges the essential group of RS domain splicing factors. Furt hermore, because no animal equivalent to this protein family has been identified to date, our results suggest that these proteins play key r oles in constitutive and alternative splicing in plants.