THE TRANS-SPLICED INTRON 1 IN THE PSAA GENE OF THE CHLAMYDOMONAS CHLOROPLAST - A COMPARATIVE-ANALYSIS

In the secondary structure model that has been proposed for the trans- spliced intron I in the Chlamydomonas reinhardtii psaA gene, a third R NA species (tscA RNA) interacts with the 5' and 3' intron parts flanki ng the exons to reconstitute a composite structure with several featur es of group-II introns. To test the validity of this model, we underto ok the sequencing and modelling of equivalent introns in the psaA gene from other unicellular green algae belonging to the highly diversifie d genus Chlamydomonas. Our comparative analysis supports the model rep orted for the C. reinhardtii psaA intron 1, and also indicates that th e 5' end of the tscA RNA and the region downstream from the psaA exon 1 cannot be folded into a structure typical of domain I as described f or most group-II introns. It is possible that a fourth RNA species, ye t to be discovered, provides the parts of domain I which are apparentl y missing.