In vitro self-splicing reactions of chloroplast and mitochondrial group-I introns in Chlamydomonas eugametos and Chlamydomonas moewusii

Abstract

The self-splicing activity of nine chloroplast group-I introns (CeLSU.1 to CeLSU.6, CepsbC.1, CepsbC.2 and CmpsaB.1) and of one mitochondrial group-I intron (CmmtLSU.1) from the interfertile green algae Chlamydomonas eugametos and C. moewusii was examined using RNA templates produced by in vitro transcription of cloned DNA sequences. All introns, with the exception of the mobile intron CeLSU.5 encoding the site-specific I-CeuI endonuclease, were found to catalyze their own splicing in the absence of proteins. The introns that proved to be the best substrates under the conditions employed are CeLSU.1, CeLSU.3, CeLSU.4, CepsbC.1 and CmmtLSU.1. The implications of our results for the origin and spread of group-I introns in the organellar genomes of green algae are discussed.