A class-I intron in a cyanelle tRNA gene from Cyanophora paradoxa: phylogenetic relationship between cyanelles and plant chloroplasts.

Cyanelles are photosynthetic organelles which are considered as intermediates between cyanobacteria and chloroplasts, and which have been found in unicellular eukaryotes such as Cyanophora paradoxa. The nucleotide sequence of a 667-bp region of the cyanelle genome from Cyanophora paradoxa containing genes coding for tRNA(UUCGlu) and tRNA(UAALeu) has been determined. The gene coding for tRNA(UAALeu) is split by a 232-bp intron which has a secondary structure typical for class-I structured introns and which is closely related to the intron located in the corresponding gene from liverwort and higher plant chloroplasts. It appears therefore that these tRNA(UAALeu) genes are all derived from one common ancestral gene which already contained a class-I intron.