Synthesis of the psbA Gene Product in Euglena

Abstract

To identify the psbA gene product of Euglena gracilis, we compared products translated in organello and in vitro. The most prominently labeled membrane protein of isolated Euglena plastids migrates as a band at 28 kilodaltons. An apparent precursor appears at 30 kilodaltons under conditions which inhibit the synthesis of cytoplasmically synthesized proteins. Translation of the 14S mRNA selected by hybridization with the Sephacryl S-500-immobilized psbA gene, however, yields products of approximately 37- and 41-kilodaltons. In organello, no significant label migrates to this region of the gel. We interpret these data to indicate that the primary translation product of Euglena psbA gene is larger than that of higher plants, but the mature, processed polypeptide is smaller.