Siberian Inst. Plant Physiol. Biochem.

Transcription as dependent on respiration and phosphorylation in isolated mitochondria --Yuri Konstantinov, Galina Lutsenko and Vladimir Podsosonny To explain the interrelationship between two main enzyme systems of maize mitochondria, the genetic system and oxidative phosphorylation (OP), the effect of different inhibitors of OP and electron transport chain on kinetics of RNA synthesis was studied in vitro in intact maize mitochondria. The characteristics of nucleotide organization of the maize mitochondrial genome and mtRNA processing suggest that transcription may be related to OP at the level of adenine nucleotide translocation, an initial step of OP, which is performed by a special protein carrier.

The inhibition of adenine nucleotide translocase by carboxyatractyloside (1µM) caused an almost two-fold decrease in the rate of 3H-UTP incorporation into the mitochondrial acid-insoluble fraction (Table 1). The inhibition of the mitochondrial electron transport chain with KCN resulted in more pronounced inhibition of RNA synthesis. The decrease in the rate of RNA synthesis in mitochondria in response to the addition of a classic OP inhibitor, oligomycin, was not so significant, amounting to about 30%. In the presence of OP uncoupler, carbonyl cyanide-m-chlorophenylhydrazone, decrease of the transcription rate was also observed.

The level of DNA-dependent synthesis of DNA did not change, but even increased when ADP was used instead of ATP as a precursor (Table 2). The transcription was strongly inhibited in this case by oligomycin indicating the direct involvement of extramitochondrial ADP after its phosphorylation into the process of RNA biosynthesis. These experimental data also suggest possible functional coupling of OP and RNA synthesis on the basis of additional microcompartments in the inner mitochondrial space.

The effect of membrane active agent, sodium cholate, on mitochondrial transcription depended on the concentrations used: low concentrations of the detergent (100µM) produced significant activation of the RNA synthesis, while higher concentrations (500µM and 1mM) showed strong inhibition effect.

It may be inferred that DNA transcription in maize mitochondria strongly depends on respiration and oxidative phosphorylation. It is assumed that the regulation mechanism of mitochondrial genome transcription may involve conformational changes in DNA-membrane complex during energy transformation in mitochondria.

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