GENES FOR COMPONENTS OF THE CHLOROPLAST TRANSLATIONAL APPARATUS ARE CONSERVED IN THE REDUCED 73-KB PLASTID DNA OF THE NONPHOTOSYNTHETIC EUGLENOID FLAGELLATE ASTASIA-LONGA

The colourless, nonphotosynthetic protist Astasia sia longa is phyloge netically related to Euglena gracilis. The 73-kb plastid DNA (ptDNA) o f A. longa is about half the size of most chloroplast DNAs (cpDNAs). M ore than 38 kb of the Astasia ptDNA sequence has been determined. No g enes for photosynthetic function have been found except for rbcL. Iden tified genes include rpoB, tufA, and genes coding for three rRNAs, 17 tRNAs, and 13 ribosomal proteins. Not only is the nucleotide sequence of these genes highly conserved between A. longa and E. gracilis, but a number of these genes are clustered in a similar fashion and have in trons in the same positions in both species. The results further suppo rt the idea that photosynthetic genes normally encoded in cpDNA have b een preferentially lost in Astasia, but that the chloroplast genes cod ing for components of the plastid translational apparatus have been ma intained. This apparatus might be needed for the expression of rbcL an d also for that of still unidentified nonphotosynthetic genes of Astas ia ptDNA.