Functional studies of mutant forms of bacteriophage T7 RNA polymerases containing point substitutions in the motif at the active site of the enzyme

: Monomeric DNA and RNA polymerases contain a number of conserved motifs. By means of random and oligonucleotide-directed mutagenesis the point mutants of bacteriophage T7 RNA polymerase containing the amino acid substitutions in motif B which is the part of the active site were obtained. The kinetic properties of the mutants were studied. The results obtained suggest that amino acid residues 636, 639 and 646 are involved in the binding of the initiating GTP, the selection of correct nucleoside triphosphate and interaction with the promoter, respectively.