SecA is plastid-encoded in a red alga: implications for the evolution of plastid genomes and the thylakoid protein import apparatus.

Partial sequence analysis of the plastid DNA (ptDNA) from a red alga, Antithamnion sp., revealed the presence of a homologue to the Escherichia coli secA gene as well as two open reading frames (ORF 510, ORF 179). In addition a sec Y homologue has been detected on the plastid genome by heterologous hybridization. None of these genes has been found in completely sequenced chlorophytic plastid genomes. SecA and secY gene copies were also detected in the ptDNA of a chromophytic alga, indicating that secA Y may be ubiquitous in rhodophytes and chromophytes. The significance of these findings for the evolution of plastid genomes and the thylakoid protein import mechanism is discussed.