Stimulation of chloroplast DNA-Dependent RNA polymerase by exogenous DNA

Abstract

In isolated chloroplasts from spinach and peas the incorporation of nucleoside triphosphates into RNA can be stimulated by the addition of calf thymus DNA. The degree of stimulation varies (25–100%) from one chloroplast preparation to another and is greater at 35 than at 25 °C. This additional incorporation of nucleoside triphosphates is shown to be due to genuine RNA synthesis. However, from DNA-RNA hybridization experiments and from experiments in which poly d(A-T) was used to stimulate RNA synthesis it is concluded that the exogenous DNA is not functioning primarily as a template for chloroplast RNA polymerase but is merely augmenting the transcription of the endogenous chloroplast DNA. In line with this conclusion is the observation that both tobacco mosaic virus RNA and the polyanion, heparin, also stimulate RNA synthesis in isolated chloroplasts. This stimulation is not attributable to the protection of the components of the reaction by the added DNA. Possible explanations for the stimulation of RNA synthesis by such polyanions are discussed.