IDENTIFICATION OF A PLANT SERINE-ARGININE-RICH PROTEIN SIMILAR TO THEMAMMALIAN SPLICING FACTOR SF2 ASF/

We show that the higher plant Arabidopsis thaliana has a serine-argini ne-rich (SR) protein family whose members contain a phosphoepitope sha red by the animal SR family of splicing factors, In addition, we repor t the cloning and characterization of a cDNA encoding a higher-plant S R protein from Arabidopsis, SR1, which has striking sequence and struc tural homology to the human splicing factor SF2/ASF, Similar to SF2/AS F, the plant SR1 protein promotes splice site switching in mammalian n uclear extracts, A novel feature of the Arabidopsis SR protein is a C- terminal domain containing a high concentration of proline, serine, an d lysine residues (PSK domain), a composition reminiscent of histones, This domain includes a putative phosphorylation site for the mitotic kinase cyclin/p34(cdc2).