Figure 3. The L173A mutant protein is stably expressed but inactive, whereas the F327A mutant has lowered protein expression.

A, Protein expression of each PKA mutant were measured. Of the two mutants that could not complement synthetic lethality in the tpk null strain, F327A also demonstrated very low protein expression. B, The catalytic activity of each PKA mutant was determined. Both L173A and F327A mutants had nearly undetectable catalytic activity.