A HIGH-RESOLUTION GENE MAP OF THE CHLOROPLAST GENOME OF THE RED ALGA PORPHYRA-PURPUREA

Extensive DNA sequencing of the chloroplast genome of the red alga Por phyra purpurea has resulted in the detection of more than 125 genes. F ifty-eight (approximately 46%) of these genes are not found on the chl oroplast genomes of land plants. These include genes encoding 17 photo synthetic proteins, three tRNAs, and nine ribosomal proteins. In addit ion, nine genes encoding proteins related to biosynthetic functions, s ix genes encoding proteins involved in gene expression, and at least f ive genes encoding miscellaneous proteins are among those not known to be located on land plant chloroplast genomes. The increased coding ca pacity of the P. purpurea chloroplast genome, along with other charact eristics such as the absence of introns and the conservation of ancest ral operons, demonstrate the primitive nature of the P. purpurea chlor oplast genome. In addition, evidence for a monophyletic origin of chlo roplasts is suggested by the identification of two groups of genes tha t are clustered in chloroplast genomes but not in cyanobacteria.