 Peak phosphorylation rates were found between the +12 to +16 amino acid distances, with a distinct increase around the +10 to +12 range and gradual decrease across the +20 to +30 range.The introduction of the -2 proline residue enhances phosphorylation both "in vitro" by expanding the peak phosphorylation range, but does not increase phosphorylation activity at distances less than +10.This expansion of the peak phosphorylation range could possibly be attributed to enhanced binding of the priming site to Cks1.