SITE-SPECIFIC MUTAGENESIS OF THE LYS-172 RESIDUE IN PHAGE T7 RNA-POLYMERASE - CHARACTERIZATION OF THE TRANSCRIPTIONAL PROPERTIES OF MUTANT PROTEINS

Leu and Gly were substituted for the Lys residue normally present at p osition 172 of bacteriophage T7 RNA polymerase (LI 72 and G172 mutants ) by the oligonucleotide-directed mutagenesis technique. Lys-172 and A rg-173 residues were also deleted (DEL172-3). The specific activity of all mutant enzymes was close to that of the wild-type enzyme. L172 an d DELI 72-3 mutants acquired the ability to synthesize RNA on template s lacking a promoter for T7 RNA polymerase. The decreased stability of the enzyme-promoter complex, as well as the alteration of the templat e specificity of these mutant proteins, was demonstrated. The possible role of the RNA polymerase interdomain 'stretch'' that includes the L ys-172 residue is discussed.