RNA splicing in Chlamydomonas chloroplasts. Self-splicing of 23 S preRNA.

The 23 S rRNA gene of the Chlamydomonas reinhardtii chloroplast contains an 888-base pair intron with structural features characteristic of Group I introns. The nuclear, chloroplast ribosome-deficient mutant of C. reinhardtii, ac20, overaccumulates a approximately 3.6-kilobase unspliced 23 S preRNA compared to wild-type cells. We have used [alpha-32P]GTP labeling of total RNA preparations from ac20 to rapidly determine that 23 S preRNA is capable of self-splicing. The ability of the 23 S intron (with flanking exon sequences) to correctly catalyze its own splicing was confirmed using RNA produced by in vitro transcription of cloned DNA. These results identify the first example of a self-splicing RNA of chloroplast origin.