Extraordinary features in the Chlamydomonas reinhardtii chloroplast genome: (1) rps2 as part of a large open reading frame; (2) a C. reinhardtii specific repeat sequence

Abstract

We have determined the DNA sequence of the 3574-bp chloroplast DNA fragment of Chlamydomonas reinhardtii formed by the overlap of BamHI fragment 3 and EcoRI fragment 5. This sequence encodes most of rps18 and orf570, an unidentified open reading frame that contains a 150 amino acid domain with high homology to the N-terminal part of 30 S ribosomal protein S2 of other chloroplast, cyanobacterial and bacterial genomes. Between these two sequences lies a highly repetitive sequence element of 500 bp, that is composed of multiple direct and inverted repeat sequences that occur in rearranged, but highly conserved form in at least 36 locations in the C. reinhardtii chloroplast genome. Among the conserved repeat sequences in the C. reinhardtii chloroplast genome we identified the borders of the inverted repeats near atpB and rps4. This might indicate that the conserved sequence elements are remainders of gene rearrangements in the chloroplast genome that occurred by relocations of the inverted repeats.