Table 1.

Repeat protein families and their characteristics

Repeat protein family	Number of amino acids in a repeat	Structural motif of a repeat	Range of numbers of repeats for natural proteins* most common number
HEAT	37–47	Two α-helices (A & B)	3–36
TPR	34	Helix-turn-helix (A & B)	3–16, 3*
Armadillo	42	Three α-helices (H1, H2, H3)	6–15, 12*
Ank	30	Helix-helix-loop (or β-hairpin) (H1, H2)	4–24, 6*
LRR	20–29	β-strand-loop-helix	Up to 28
WD40	40–60	Four-stranded (a–d) antiparallel β-sheet	3–16, 7*–8*

Names for protein families originate from: HEAT, Huntingtin; Elongation factor 3; A subunit of PP2A; lipid kinase TOR; TPR, tetratricopeptide repeat; Armadillo, the appearance of embryos that are mutant for the Drosophila segment polarity gene armadillo; Ank, ankyrin-like repeat; LRR, leucine rich repeat; WD40 (also known as WD or beta-transducin repeats) amino acid motifs, often terminating in a Trp-Asp (WD) dipeptide.