A sequence of about thirty to forty amino-acid residues long found in the sequence of epidermal growth factor (EGF)has been shown [<cite idref="PUB00001077"/>, <cite idref="PUB00001555"/>, <cite idref="PUB00003983"/>, <cite idref="PUB00004321"/>, <cite idref="PUB00004609"/>] to be present, in a moreor less conserved form, in a large number of other, mostly animal proteins. The list of proteins currently known tocontain one or more copies of an EGF-like pattern is large and varied. The functional significance of EGF domains inwhat appear to be unrelated proteins is not yet clear. However, a common feature is that these repeats are found inthe extracellular domain of membrane-bound proteins or in proteins known to be secreted (exception: prostaglandinG/H synthase). The EGF domain includes six cysteine residues which have been shown (in EGF) to be involved in disulphidebonds. The main structure is a two-stranded beta-sheet followed by a loop to a C-terminal short two-stranded sheet.Subdomains between the conserved cysteines vary in length.