The DNA fragment Eco-I (4700 kilobasepairs) from the circular chloroplast genome of Euglena gracilis is shown to be transcribed in etioplasts at all stages of light-induced plastid development and in fully differentiated chloroplasts. Major stable transcription products are mRNAs of 14S and 17S. Using a rabbit reticulocyte lysate translation system we can show that the fragment Eco-I selects a mRNA which directs the synthesis of a M r 32 000–33 000 polypeptide. Eco-I also hybridizes with a 330 basepair DNA probe cut from within the spinach chloroplast gene encoding the M r 32 000 thylakoid membrane protein of the photosystem II reaction center. We conclude that the fragment Eco-I carries the corresponding Euglena gracilis chloroplast gene.
