Analysis of the 22 kbp long <i>psb</i>D-<i>psb</i>C gene cluster of <i>Euglena gracilis</i> chloroplast DNA : Evidence for overlapping transcription units undergoing differential processing

The clustered genes <i>psb</i>D and <i>psb</i>C covering together close to 22000 nucleotides contain ten and eleven exons, respectively. The corresponding translation products, i.e, Photosystem II core 34 kDa (D2) protein and the CP43 chlorophyll binding protein are highly conserved. Introns vary in lenght from 305 to 4144 nucleotides. The two genes have about 900 nucleotides in common including an intron. To obtain stable mRNAs of about 1400 (<i>psb</i>D) and 1500 (<i>psb</i>C) nucleotides the pre-transcripts must undergo differential processing and/or splicing events within the overlapping region.