Self-splicing of the Chlamydomonas chloroplast psbA introns.
We used alpha-32P-GTP labeling of total RNA preparations to identify self-splicing group I introns in Chlamydomonas. Several RNAs become labeled with alpha-32P-GTP, a subset of which is not seen with RNA from a mutant that lacks both copies of the psbA gene. Hybridization of the GTP-labeled RNAs to chloroplast DNA indicates that they originate from the psbA and rrn 23S genes, respectively, the only genes known to contain group I introns in this organism. Introns 1, 2, and 3 of psbA (with flanking exon sequences) were subcloned and transcribed in vitro. The synthetic RNAs were found to self-splice; splicing required Mg2+, GTP, and elevated temperature. In addition, the accuracy of self-splicing was confirmed for introns 1 and 2, and intermediates in the splicing reactions were detected. These results, together with our recent data on the 23S intron, indicate that the ability to self-splice is a general feature of Chlamydomonas group I introns. These findings have significant implications for the mechanism of group I intron splicing and evolution in Chlamydomonas and other chloroplast genomes.
Herrin
D L
DL
Department of Botany, University of Texas, Austin 78713.
Bao
Y
Y
Thompson
A J
AJ
Chen
Y F
YF
D000818:Animals; D001483:Base Sequence; D002696:Chlamydomonas / Q000235:genetics*; D002736:Chloroplasts / Q000378:metabolism; D015342:DNA Probes; D016054:DNA, Protozoan / Q000235:genetics; D007438:Introns; D008969:Molecular Sequence Data; D012326:RNA Splicing; D016053:RNA, Protozoan / Q000235:genetics
D015342:DNA Probes; D016054:DNA, Protozoan; D016053:RNA, Protozoan