On the mechanism of streptolydigin inhibition of Escherichia coli RNA polymerase.

The mechanism of streptolydigin inhibition of RNA synthesis has been investigated with a combination of steady state kinetics and product analysis by employing the abortive initiation reaction of Escherichia coli RNA polymerase. The pattern of inhibition by streptolydigin on the poly[d(A-T)] . poly[d(A-T)]template (non-competitive versus AMP; competitive versus UTP) was consistent with one inhibitor binding site and with an ordered addition of AMP followed by UTP. The more complicated patterns observed on the poly[d(I-C)] . poly[d(I-C)] template and the bacteriophage T7 A2 promotor (noncompetitive versus CTP) were explained by assuming that streptolydigin could stabilize the translocated ternary complex containing the product dinucleotide. Product analysis of two other abortive initiation reactions showed that the product did not dissociate from the inhibitor-bound translocated ternary complex. Finally, rifampicin and streptolydigin were shown to be functionally independent during initiation on several templates.