Intron-specific RNA binding proteins in the chloroplast of the green alga Chlamydomonas reinhardtii

Mitochondria and chloroplasts both contain group II introns which are belie ved to be the ancestors of nuclear spliceosomal introns. We used the mitoch ondrial group II intron rI1 from the green alga Scenedesmus obliquus for bi ochemical characterization of intron-specific RNA binding proteins. rI1 is correctly spliced from a chloroplast precursor RNA when integrated into the chloroplast genome of Chlamydomonas reinhardtii. Glycerol gradients reveal ed the sedimentation profile of transcripts containing intron rI1 in native C. reinhardtii extracts and in deproteinized RNA preparations, thus indica ting the association of rI1 containing transcripts with high molecular weig ht ribonucleoprotein complexes in vivo. Furthermore, the specific binding o f a 61 kDa protein and a 31 kDa protein with the conserved domain IV-was de monstrated using a set of intron derivatives for in vitro RNA binding exper iments. We propose that we have biochemically characterized 'general splici ng factors', which enable the successful splicing even of mitochondrial int rons in chloroplasts. (C) 2001 Elsevier Science B.V. All rights reserved.