Evidence for two RNA polymerase activities in Euglena gracilis chloroplasts

Two types of RNA polymerase activity were isolated from Euglena gracilis chloroplasts and compared. One polymerase is tightly bound to chloroplast DNA; this complex is called the transcriptionally active chromosome (TAC) (Rushlow, K. E., Orozco, E. M., Jr., Lipper, C., and Hallick, R. B. (1980) J. Biol. Chem. 255, 3786-3792). The other activity is found in a soluble extract of Euglena chloroplasts. The soluble extract is dependent upon an exogenous DNA template for activity. The two activities can be isolated in two distinct subchloroplast fractions from a single chloroplast preparation. The soluble extract is selective for transcription of transfer RNA genes, whereas the TAC is selective for ribosomal RNA genes. TAC and the soluble extract respond differently to KCl and Mg2+. The soluble extract is sensitive to heparin, and TAC is resistant. The two activities have different temperature optima. Based on this evidence, we conclude that Euglena chloroplasts have at least two distinct RNA polymerase activities.