Conserved residues implicated in peptide-substrate recognition. Consensus motifs for the catalytic loop region in subdomain VIB and activation loop region in subdomain VIII were determined for the members of each of the seven major ePK groups with known or likely kinase activity. Invariant residues at a given position are indicated by single upper-case letters. Two upper-case letters at a single position indicate that either of two residues are strictly conserved, the most frequent shown in the top row. Positions in which more than two amino acids are present are indicated with lower-case letters; a single letter indicates that only one residue is highly conserved, two letters indicate that either of two residues are frequently conserved (most frequent on the top row), and 'x' indicating poor positional conservation. Residues highlighted in outline are notably conserved within an ePK group and are thought to function in the recognition of peptide substrates specifically targeted by the members of the group.