Compositions and methods for inhibition of the intracellular activation of a signal transducing protein comprising phosphoserine containing peptides derived from the Raf-1 protein are disclosed. The peptides bind to 14-3-3 protein and thereby prevent its association with the signal transducing peptide to block signal transduction. Also provided is an assay method for identifying a pharmacologic agent that can bind 14-3-3 protein and block signal transduction.