Enrichment of matches to the CDK consensus in CDK substrates. (a) The protein sequences of well characterized ('known') CDK targets (gray bars) are highly enriched for matches to the CDK strong consensus relative to the genome (black bars) but not for a scrambled version of the consensus. Similar results hold for the 'unbiased positives' from a high-throughput study (unfilled bars). (b) 'Known' and 'unbiased positives' are also somewhat enriched for the weak consensus but not for a scrambled version of it. See text for details. Frequencies are number of matches per 1000 amino acid (aa) residues. Error bars represent plus or minus two times the standard error. CDK, cyclin dependent kinase.