Chloroplast preparations from the young primary leaves of Phaseolus vulgaris L. cv. Canadian Wonder carry out the DNA-dependent incorporation of UTP into RNA at rates between 8 and 14 pmol UTP μg−1 chlorophyll h−1. It is estimated that 90% of the activity was localized in the chloroplasts. The incorporation proceeded for between 20 and 30 min at 35 °C. The maximum rates of RNA synthesis were attained at pH 8.3, in the presence of 15 mM MgCl2. Chloroplasts were also active, to a lesser extent, with 1.5 mM MnCl2. The simultaneous presence of MnCl2 and MgCl2 resulted in inhibition of activity. Nuclear material prepared from young P. vulgaris leaves incorporated UTP at a rate of about 12 pmol UTP μg−1 DNA h−1. On a chloroplast (Tritonsoluble) DNA basis chloroplast activity was over 40-fold that of nuclei. Methods of solubilizing chloroplast RNA polymerase were explored. Yields of over 75% were achieved, but methods suitable for one species were not always successful when applied to another. The highest yields of the P. vulgaris enzyme were obtained using EDTA and KCl. All methods resulted in solubilization of DNA. RNA synthesis by the soluble P. vulgaris enzyme proceeded for more than 40 min at 35 °C.
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Ness et al. (1980) studied this question.