Identification of an RNA-protein complex involved in chloroplast group II intron trans-splicing in Chlamydomonas reinhardtii

In Chlamydomonas reinhardtii, the psaA mRNA is assembled by a process invol ving trans-splicing of separate transcripts, encoded at three separate loci of the chloroplast genome, At least 14 nuclear loci and one chloroplast ge ne, tscA, are needed for this process. We have cloned Raa3, the first nucle ar gene implicated in the splicing of intron 1. The predicted sequence of R aa3 consists of 1783 amino acids and shares a small region of homology with pyridoxamine 5'-phosphate oxidases, Raa3 is present in the soluble fractio n of the chloroplast and is part of a large 1700 kDa complex, which also co ntains tscA RNA and the first psaA exon transcript. These partners, in asso ciation with other factors, form a chloroplast RNP particle that is require d for the splicing of the first intron of psaA and which may be the counter part of eukaryotic snRNPs involved in nuclear splicing.