GENE STRUCTURE AND EXPRESSION OF A NOVEL EUGLENA-GRACILIS CHLOROPLASTOPERON ENCODING CYTOCHROME B6 AND THE BETA-SUBUNIT AND EPSILON-SUBUNIT OF THE H-ATP SYNTHASE COMPLEX()

The genes encoding cytochrome b6 of the chloroplast cytochrome b6/f co mplex (petB) and the ATP synthase CF1-beta subunit (atpB) and epsilon- subunit (atpE) were identified on the EcoD fragment of the Euglena gra cilis chloroplast genome. The complete nucleotide sequence of these th ree genes was determined. The petB-atpB-atpE genes are cotranscribed a s a tricistronic operon. This gene organization differs from that of l and plants in which atpB- atpE form a discistronic operon, and petB is within the psbB-ycf8-psbH-petB-petD operon. Euglena cytochrome b6 and the beta-subunit of the chloroplast ATP synthase are very similar in derived amino acid sequence to the corresponding gene products from ot her organisms. The epsilon-subunit of the chloroplast ATP synthase com plex is more divergent. In Euglena, the petB-atpB-atpE genes contain i ntrons, including two twintrons, at eight different positions. All of the intron positions were confirmed by analysis of cDNAs. Two independ ent intercistronic RNA processing events and 11 splicing reactions lea d to the accumulation of the mature petB, atpB and atpE monocistronic mRNAs.