Rearrangement of chloroplast ribosomal cistrons by unequal crossing-over in Euglena gracilis.

The chloroplast DNA of a wild type photosynthetic variant of Euglena gracifs (ATCC n° 10616) with five ribosomal cistrons has been analyzed by restriction mapping. The results complete the electron microscope study of Koller and Delius (MGG 188, 305, 1982); they support a model of formation of the variant DNA by rearrangement of the wild type ribosomal cistrons through unequal crossing-over. The recombination sites have been determined. The recombination model proposed also explains the formation of the "Z-S" variant with a single ribosomal cistron (Wurtz and Buetow 1981).