FUNCTIONAL-STUDY OF BACTERIOPHAGE-T7 RNA-POLYMERASE MUTANT FORMS CONTAINING POINT AMINO-ACID SUBSTITUTIONS IN MOTIF B OF THE ENZYME ACTIVE-CENTER

Monomeric DNA and RNA polymerases contain a number of common structura l motifs. The properties of several mutant T7 bacteriophage RNA polyme rase forms obtained by random and oligonucleotide-directed mutagenesis have been investigated. The mutant enzyme forms contain amino acid su bstitutions in the region of structural motif B which is a part of the enzyme active center. Their kinetic parameters suggest that amino aci d residue 636 participates in binding of initiating GTP and that resid ues 639 and 646 are involved in selection of the complementary NTP and interaction with promoter, respectively.