ROLE OF OPEN COMPLEX INSTABILITY IN KINETIC PROMOTER SELECTION BY BACTERIOPHAGE-T7 RNA-POLYMERASE

By measuring steady-state rates of dinucleotide synthesis on double-st randed (d.s.) and partially single-stranded (p.s.s.) promoters, and to pological unwinding due to open complex formation on plasmids, we have obtained evidence that open complex formation in bacteriophage T7 RNA polymerase:promoter binary complexes is thermodynamically disfavored and that the rate of collapse of the open complex is competitive with the rate of transcription initiation. It is suggested that open comple x instability is a kinetic mechanism that allows T7 RNA polymerase (RN AP) to achieve promoter specificity while still allowing for efficient promoter release. Open complex instability could also provide a mecha nism for modulating the K-M for the initiating NTPs so as to allow dif ferent promoters to respond differently to physiological changes in NT P concentration. (C) 1997 Academic Press Limited.