The large ribosomal protein gene cluster of a cryptomonad plastid: Gene organization, sequence and evolutionary implications

The complete sequence of the major ribosomal protein gene cluster of the plastid genome of the cryptomonad alga Guillardia theta (formerly Cryptomonas Φ) is presented. The ribosomal protein genes (corresponding to the SIO, spc, alpha and L13/S9 operons of E. coli are found upstream of the previously reported plastid str operon, and transcribed in the same orientation. The genes are very tightly packed with as little as two nucleotides between the rpll4 and rpl24 genes. The gene arrangement is very similar to that reported for the rhodophyte alga, Porphyra purpurea, and the chromophyte diatom, Odontella sinensis, indicating a close evolutionary relationship between these groups of algae. Northern analysis indicates that the 29 genes1 are arranged as one operon and are transcribed as a single mRNA that is subsequently processed into smaller transcripts.