On the functional role of the Tyr‐639 residue of bacteriophage T7 RNA polymerase

Abstract
Substitution or Asp for a Tyr residue normally present at position 639 of the bacteriophage T7 RNA polymerase leads to a drastic drop in the enzymatic activity. This mutation does not affect the enzyme‐promoter interaction but decreases the ability of the RNA polymerase to discriminate between GTP and ATP molecules, resulting in a decrease in the rate of the incorporation of the nucleotide into the RNA chain.