TWINTRONS ARE NOT UNIQUE TO THE EUGLENA CHLOROPLAST GENOME - STRUCTURE AND EVOLUTION OF A PLASTOME CPN60 GENE FROM A CRYPTOMONAD

Introns within introns (twintrons) are known only from the Euglena chl oroplast genome. Twintrons are group II or III introns, into which ano ther group II or III intron has been transposed. In this paper we desc ribe a non-Euglena twintron structure within a plastid-encoded chapero ne gene (cpn60) of the cryptomonad alga Pyrenomonas salina. In additio n, the evolutionary relationships between members of the Cpn60 protein family are determined. Our findings permit the inclusion of cryptomon ad plastomes in phylogenetic studies of intron evolution and present f urther evidence for the origin of modern plastids from a cyanobacteria l ancestor.