Subunit structure of DNA-dependent RNA polymerase of Anacystis nidulans

Specific initiation of transcription at a cyanobacterial promoter with RNA polymerase purified from Calothrix sp. PCC 7601

Although in cyanobacteria many genes have been shown to be transcriptionally controlled by specific stimuli, little is known about promoter structure and the form of RNA polymerase that recognizes individual promoters. RNA polymerase holoenzyme has been purified from Calothrix sp. PCC 7601. Its polypeptide composition resembles that of the plant chloroplast enzymes. To study transcription in cyanobacteria further, we have analysed the promoter-recognition properties of the purified enzyme. In vitro transcription was assayed with the promoter of the phycocyanin gene (cpc1) that is expressed whatever the incident light conditions. Transcription initiation at the same start point as in vivo was obtained with the Calothrix sp. PCC 7601 purified enzyme and the Escherichia coli core enzyme supplemented with a Calothrix sp. PCC 7601 sigma factor, but not with the E. coli holoenzyme.

Functional hybrid enzymes reconstituted from Escherichia coli and Serratia marcescens RNA polymerase subunits

RNA polymerase was isolated from Escherichia coli and Serratia marcescens. The subunits of both enzymes were separated by electrophoresis on cellulose acetate sheets in the presence of urea. Under conditions favouring reconstitution of the RNA polymerases, stoichiometric amounts of the subunits were allowed to interact. Active hybrid enzymes were formed if corresponding subunits of both enzymes were mutually exchanged. The analysis of the RNA products synthesized showed that the reconstituted enzymes are able to recognize the promoters for transcription and the termination signals on the DNA template. The transcription products can serve as messengers for cell-free protein synthesis.

The reconstitution of Anacystis nidulans DNA-dependent RNA polymerase from its isolated subunits

The DNA-dependent RNA polymerase of the blud-green alga Anacystis nidulans was reconstituted from its isolated subunits in the absence of urea. Applying this technique the kinetics and the subunit requirements of the reconstitution process were analyzed. The results reveal differences with respect to the reconstitution of Escherichia coli polymerase. Reconstitution proceeds much more slowly in the case of the A. nidulans enzyme. Reconstitution here is absolutely dependent on the presence of the subunit sigma. On the other hand, the largest of the subunits of Mr=190000 can be fully substituted by a specific degradation product of this subunit of Mr=175000. 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 procaryotic organisms.

Properties and subunit composition of RNA polymerase II from plant cell cultures

The purification of DNA-dependent RNA polymerase II (EC 2.7.7.6) from plant cell cultures of Petroselinum (parsley) is described. The procedure during which enzyme I is eliminated includes initial precipitation with (NH4)2SO4, an ultracentrifugation step, gel filtration on Sepharose 4B, chromatography on DEAE-cellulose, DNA-agarose and DEAE-Sephadex. The enzyme purified almost to homogeneity exhibits maximal activity with denatured DNA, and is activated preferentially by Mn2+; alpha-amanitin acts as a strong inhibitor. Electrophoresis of the enzyme in the presence of dodecylsulphate indicates that it is composed of seven subunits with mol. wts of 200 000, 180 000, 140 000, 43 000, 26 000, 25 000 and 16 000. The results of molecular weight and molar ratio determinations suggest that Petroselinum RNA polymerase II may exist in two active forms differing only in the composition of their high molecular weight subunits.