Complete gene map of the plastid genome of the nonphotosynthetic euglenoid flagellate Astasia longa

Abstract

Astasia longa is a colourless heterotrophic flagellate closely related to the photoautotrophic Euglena gracilis. A circular 73 kb plastid DNA (ptDNA) has been isolated from A. longa that is about half the size of the chloroplast DNA of E. gracilis (143 kb). We have determined the complete sequence of the ptDNA of A. longa and established a complete gene map. All chloroplast genes for photosynthesis-related proteins are completely absent from the A. longa plastid DNA except for rbcL, the gene for the ribulose-1,5-bisphosphate carboxylase large subunit. Identified genes encode components of the plastid transcriptional and translational machinery: genes for three subunits of a chloroplast RNA polymerase, 20 chloroplast ribosomal protein genes, a gene for a plastid elongation factor Tu, 27 plastidic tRNA genes and three tandemly arranged repeats of 16S, 23S and 5S rDNA. Transcripts of a number of genes were detected by Northern hybridisation. The ribulose-1,5-bisphosphate carboxylase large subunit protein has been identified by immunoblotting.