The cyanelle str operon from Cyanophora paradoxa: sequence analysis and phylogenetic implications

The str operon containing the genes for the ribosomal proteins S12 (rps12) and S7 (rps7) and for the elongation factors G (fus) and Tu (tufA) has been characterized for some cyanobacteria and chloroplasts from algae and higher plants. In the case of plastids a stepwise reduction by one and two genes, respectively, has been observed due to gene transfer to the nuclear genome. The nucleotide sequence of the str operon on the cyanelle genome from Cyanophora paradoxa was determined as a first example for a chlorophyll b-less plastid. It comprises rps12, rps7 and tufA which are closely linked and not interrupted by introns. Transcript analysis revealed cotranscription of the two ribosomal protein genes whereas tufA gave rise to a monocistronic mRNA. Phylogenetic studies using these three different traits allowed an assessment of the position of Cyanophora paradoxa among oxygenic photoautotrophs.