Family of short repeats that occurs in a limited number of membrane proteins. It may divide further in short repeats of around 7-10 residues of the pattern G-#-X(2)-#(2)-X (#=hydrophobic).

1: New Knowledge from Old: In silico discovery of novel protein domains in Streptomyces coelicolor. Yeats C, Bentley S, Bateman A; BMC Microbiol 2003;3:3-3. PMID:12625841