Direct measurement of absolute suppressor efficiency.

We have devised a system for measuring the degree of translational readthrough past a nonsense mutation which is based upon the quantitation of the two translation products, the suppressed polypeptide and the nonsense fragment. The absolute efficiency of four different amber suppressors (Su1, Su2, Su3, and Su7) has been determined at two unique amber sites in the structural gene for the beta subunit of Escherichia coli RNA polymerase.