Abstract
Interorganellar regulatory interactions in the flagellate Euglena gracilis were shown to be more complicated than in green algae and higher plants. Euglena plastids have a much more complex influence on nuclear gene expression than was previously thought. The petJ gene for cytochrome c6 represents a group of nucleus-encoded genes for chloroplast proteins, the expression of which is influenced by the state of plastids at the transcriptional level. Moroever, the regulation of these genes might be light-dependent. In contrast, for nucleus-encoded small subunit of ribulose-bisphosphate carboxylase, chlorophyll a/b binding protein, and porphobilinogen deaminase transcript levels are unchanged in wild-type cells relative to white mutants. In these cases there is no plastid-derived signal operative during transcription. Porphobilinogen deaminase appeared to be regulated even at the post-translational level.