Output of the ScanProsite web page. (a) The left protein is a classical ephrin receptor protein (ephrin B4 receptor protein) which is known to transduce a signal through its kinase domain (5). The right protein is also an ephrin receptor protein (human ephrin B6 receptor protein) but with an inactive kinase domain (6). The ProRule associated with the kinase domain identifies an active site in ephrin B4 receptor but not in ephrin B6 receptor (absent feature: active site). The canonical Asp residue at the active site position is replaced by a serine. (b) We used ScanProsite to identify orthologues of the ephrin B6 receptor in mammals, searching for proteins that have the same domain arrangement and have a putative inactive kinase domain. (c) We also identified with ScanProsite an uncharacterized plant subfamily of kinase receptors with a putative inactive kinase domain. The canonical aspartate residue at the active site position is replaced by a histidine. This kinase subfamily is conserved in various plant genomes. Both multiple sequence alignments were generated on the ScanProsite web page using the alignment with the kinase profile (PS50011).