[Kinetics of inhibition by 8-oxy-GTP and 8-bromo-GTP of Escherichia coli RNA-polymerase synthesis of pppApU dinucleotide on the promotor a1 of phage T7deltaD111 DNA in a limited set of substrates].

Detailed analysis of the kinetics of inhibition of E. coli RNA-polymerase-catalyzed synthesis of dinucleotide pppApU by 8-oxy-GTP and 8-Br-GTP on promoter A1 of the bacteriophage T7 delta D111 with an incomplete set of substrates was carried out. In accordance with the mathematical models obtained, we calculated quantitative parameters of binding of these nucleotide analogs to the centers whose geometry is suitable for incorporation of ATP and UTP. 8-oxy-GTP and 8-Br-GTP compete with ATP for the binding center (their steady-state dissociation constant ratios are 2.1 and 2.4, respectively, whereas the constant for ATP is 0.3 mM) but, unlike ATP, they are not incorporated into the product. 8-oxy-GTP competes also with UTP (its steady-state dissociation constant ratio is 21.6, the constant for UTP is 0.03 mM). 8-Br-GTP does not interact with the binding center of UTP.