An isolated multiprotein complex of S. cerevisiae components is provided
that is effective to modulate peptidyl transferase activity during translation.
This complex includes a Modulator of Translation Termination protein (Mtt1p, also
referred to as helicase B), a Upf1 protein, a peptidyl eukaryotic release factor
1 (eRF1) and a peptidyl eukaryotic release factor 3 (eRF3).