The ribosomal RNA repeats are non-identical 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 Porphyra purpurea has been constructed. Southern hybridization experiments 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 regions 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 intramolecular recombination between the repeats can be detected. We discuss the possibility that the chloroplast genome of P. purpurea is organized like that of the ancestral chloroplast.