[Influence of ionic strength on RNA-polymerase structure].

Chromatography of RNA polymerase holoenzyme preincubated under different ionic strength conditions on the DNA agarose column was studied. Ratio of two peaks identified to be core and holoenzyme was analysed. In the range of 0.15 to 0.05 M KCl the relative content of the holoenzyme peak gradually decreased from 100 to 50%. At the same time a peak of free sigma-subunit appeared as detected by the chromatography on DNA agarose gel A-1.5 m. The dissociation of half of the sigma-subunit amount occured within the enzyme dimer-monomer transition range. The results suggest that the dimerization follows the equation: E sigma + E sigma in equilibrium with E2 sigma. Reconstitution of the RNA polymerase holoenzyme from purified core enzyme and sigma-subunit was also studied by the same method. Reconstitution did not occur at a low ionic strength (0--0.1 M KCl), but takes place at ionic strength of 0.2 M or higher. Possible function of the dimerisation of the enzyme in search of promoter site and regulation of RNA synthesis is discussed.