TRANSCRIPTION ACTIVITY OF A DNA-PROTEIN COMPLEX ISOLATED FROM SPINACH PLASTIDS

A DNA · protein complex of about 150 S is isolated from purified spinach chloroplasts by Sepharose 4B gel filtration. A DNA‐dependent RNA polymerase activity is found associated with the complex. This DNA · protein complex is able to initiate RNA chains in vitro. The RNA synthesis is more dependent on CTP than other nucleoside triphosphates. 50% of the activity is still present with 0.6 M KCl. The temperature optimum occurs between 30°C and 35°C. Rifampicin and rifamycin SV have no inhibitory effect. RNA products have been characterized by gel filtration and by hybridization with chloroplast DNA (ctDNA). At the beginning of transcription RNA products are linked to the transcription complex and are later detached. The molecular weight of the product ranges between 0.07 × 106 and 2 × 106. A part of the product (3–4%) has a molecular weight higher than 2 × 106. No endogenous RNase activity was present during the molecular weight determination experiments. Hybridization experiments show that at least 75% of the RNA products are hybridizable with ctDNA and that 40% of these products are composed of chloroplast ribosomal RNA, showing that rDNA is preferentially transcribed. Copyright © 1979, Wiley Blackwell. All rights reserved