THE RIBOSOMAL-RNA REPEATS ARE NONIDENTICAL AND DIRECTLY ORIENTED IN THE CHLOROPLAST GENOME OF THE RED ALGA PORPHYRA-PURPUREA

A detailed restriction map of the chloroplast genome of the red alga P orphyra purpurea has been constructed. Southern hybridization experime nts with cloned or gel-purified restriction fragments and PCR products indicate that the P. purpurea chloroplast genome is approximately 188 kb in size. This circular molecule contains two rRNA-encoding repeats (approximately 4.9 kb) that separate the genome into single-copy regi ons of 34 kb and 144 kb. Interestingly, these repeats are arranged in a direct orientation. In addition, DNA sequencing of the ends of both repeats revealed that the two-rRNA repeats are not identical. No intra molecular recombination between the repeats can be detected. We discus s the possibility that the chloroplast genome of P. purpurea is organi zed like that of the ancestral chloroplast.