The single-nucleotide polymorphism (SNP) L94M favors the formation of heterodimers with hairy and enhancer of split 1 (HES1) and hairy/enhancer-of-split related with YRPW motif 1 (HEY2). (a) The helix-loop-helix domain of HEY1, HEY2, HEYL, HES1 and Myc-associated factor X (MAX) were aligned by ClustalW2 and formatted with BOXSHADE. Identical amino acids are in black, and conserved residues are in gray. The asterisk indicates the conserved leucine residue at position 94 in HEY1. (b) Whole-cell extracts from COS-1 cells previously transfected with expression vectors for flag-tagged HEY1, the variant L94M or HES1 were incubated with glutathione S-transferase (GST) fusion proteins of HEY1 or the variant L94M coupled with Sepharose beads. The associated proteins were detected by western blotting using anti-Flag antibody. (c) Whole-cell extracts from COS-1 cells previously transfected with expression vector for Flag-tagged HEY2 were incubated with GST fusion proteins of HEY1 or the variant L94M coupled with Sepharose beads. The associated proteins were detected by western blotting using anti-Flag antibody.