Peptide library analysis of PAK6 phosphorylation site specificity.

<p>Left panel, relative phosphorylation levels of 201 peptide mixtures within a positional scanning peptide library by PAK6. PAK6 was incubated with the peptide mixtures in the presence of [γ-³³P]ATP, and radiolabel incorporation was assessed by phosphor imaging. A representative image of two replicates is shown. Right panel, positively selected amino acid residues at each position. Quantified spot intensities from two separate runs were background corrected and then normalized so that the average value within a position was 1.0. Residues with normalized selectivity values greater than 1.6 are shown. Values are the mean of two runs. An asterisk indicates strong apparent selection for Ser that may be an artifact due to peptide mixtures with fixed Ser residues having two potential sites of phosphorylation.