ORGANIZATION OF CHLOROPLAST RIBOSOMAL-RNA GENES AND IN-VITRO SELF-SPLICING ACTIVITY OF THE LARGE SUBUNIT RIBOSOMAL-RNA INTRON FROM THE GREEN-ALGA CHLORELLA-VULGARIS C-27

Sequencing of the rRNA gene (rrn) cluster of Chlorella vulgaris C-27 c hloroplasts has revealed a striking organizational difference in compa rison to another species of the same genus, Chlorella ellipsoidea C-87 . The rrn23 gene in C. vulgaris is also split. However, the 815-bp int ervening sequence in this gene has been identified as a group-I intron . An in vitro rrn23 transcript containing the entire intron and parts of flanking exon sequences is able to self-splice in vitro in the pres ence of GTP and Mg++. Accurate ligation of the exons has been confirme d by sequencing the cDNA of the spliced products. GTP labelling of tot al Chlorella RNA in vitro has revealed that the number of self-splicin g RNAs present in Chlorella chloroplasts is limited compared to that f ound in other green algal species.