<p>The NHL repeat was defined by amino acid sequence homologies among Ncl-1, HT2A and Lin-41 proteins [<cite idref="PUB00005488"/>]. NHL is a conserved structural motif present in a large family of growth regulator. Many NHL containing proteins have additional domains such as a RING finger, a B-box zinc finger or a coiled-coil motif. According to structural model analysis the NHL domain could be involved in protein-protein interaction [<cite idref="PUB00017037"/>]. </p><p>The NHL domain is a six-bladed beta-propeller, with the blades arrayed in a radial fashion around a central axis, and each blade composed of a highly twisted four stranded antiparallel beta-sheet [<cite idref="PUB00017037"/>]. The innermost strand of each blade is labeled 'a' and the outermost strand, 'd'. Like in other beta-propellers the sequence repeats are offset with respect to the blades of the propeller, such that any given 40-residue NHL repeat spans strands 'b-d' of one propeller blade and strand 'a' of the subsequent blade. This offset ensures circularization of the propeller because the last strand of the final sequence repeat acts as an innermost strand a of the blade that harbors strands 'b-d' from the first sequence repeat. </p> NHL repeat, subgroup