Organization of chloroplast ribosomal RNA genes and in vitro self-splicing activity of the large subunit rRNA intron from the green alga Chlorella vulgaris C-27

Abstract

Sequencing of the rRNA gene (rrn) cluster of Chlorella vulgaris C-27 chloroplasts has revealed a striking organizational difference in comparison to another species of the same genus, Chlorella ellipsoidea C-87. The rrn23 gene in C. vulgaris is also split. However, the 815-bp intervening 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 presence of GTP and Mg⁺⁺. Accurate ligation of the exons has been confirmed by sequencing the cDNA of the spliced products. GTP labelling of total Chlorella RNA in vitro has revealed that the number of self-splicing RNAs present in Chlorella chloroplasts is limited compared to that found in other green algal species.