Mechanism of action of RNA polymerase on Z DNA

B to Z transition of poly(dGdC) x poly(dGdC) and poly(dGdm/sup 5/C) x poly(dGdm/sup 5/C), induced by cations, produces parallel reduction in template activity with E. coli RNA polymerase (RNAP). They now find, using the methylated polymer, that both initiation (..gamma.. /sup 32/P-GTP incorporation) and elongation (CTP incorporation) are inhibited on the Z form. When Z was stabilized at a (Co(NH/sub 3/)/sub 6/)/sup 3 +/ concentration well beyond that necessary for the transition, disproportionately greater loss in elongation occurred, indicating elongation was limiting. However, stabilizing Z only marginally at a Mg/sup 2 +/ concentration just beyond that required for the transition, they have found proportionate loss in initiation and elongation. They also find RNAP-concentration-dependent perturbation of the circular dichroism of the Z form of methylated and unmethylated polymers to spectra characteristic of mixtures of B and Z, indicating partial reformation of B and suggesting that RNAP binds better to that form. Preliminary studies of RNAP binding to the methylated polymer by sedimentation in an analytical ultracentrifuge indicate that highly stabilized Z as well as B binds RNAP, but that B binds more RNAP than Z.