The Reconstitution of Anacystis nidulans DNA‐Dependent RNA Polymerase from Its Isolated Subunits

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Abstract
The DNA-dependent RNA polymerase of the blue-green alga A. nidulans was reconstituted from its isolated subunits in the absence of urea. The kinetics and the subunit requirements of the reconstitution process were analyzed. Differences with respect to the reconstitution of Escherichia coli polymerase were revealed. Reconstitution proceeds much more slowly in the case of the A. nidulans enzyme. Reconstitution is absolutely dependent on the presence of the subunit .sigma.. The largest enzyme subunit (Mr [molecular weight] = 190,000) can be fully substituted by a specific degradation product of this subunit (Mr = 175,000). Heterologous reconstitution between subunits of E. coli and A. nidulans polymerase does not result in active enzyme hybrids, showing a divergent evolution of the structure of this enzyme in these prokaryotic organisms.