Tyr-571 is involved in the T7 RNA polymerase binding to its promoter.

The in vitro studies of three T7 RNA polymerase point mutants suggest that substitutions of Ala and Thr for Pro-563 and of Ser for Tyr-571 have little effect on the enzyme catalytic competence, but result in its inability to utilize the promoter. Both P563A and P563T mutants retain the promoter-binding ability, whereas the promoter affinity of the Y571S mutant drops drastically.