Fig. 1. Structure of AMER1, AMER1(short) and AMER2, and their interaction with the ARM repeats of APC. (A) Scheme of human AMER1, AMER1(short) and AMER2. The APC-interacting sequences are indicated by gray shading. In AMER1(short), the C-terminal amino acids that are different from AMER1 are indicated in black. (B) Amino acid sequence of human AMER1 and AMER1(short). APC-interacting sequences are shaded, glutamic acid-rich and proline-rich sequences are underlined, and the REA repeats are in italics. For AMER1(short), only the amino acids from position 786 onwards, which are different to AMER1, are shown. This sequence is encoded by a separate 3' exon (see text for details). (C, upper panel) Interaction of murine Amer1 sequences #1-3 with the human APC ARM repeat region (APC-ARM) as well as with an asparagine-to-lysine substitution mutant (APC-ARM^N507K) in quantitative yeast two-hybrid assays. The seven ARM repeats are indicated by shaded boxes. Values represent -galactosidase units of representative experiments. (C, lower panel) Interaction of human AMER2 APC-binding sites #1 and 2 with APC-ARM in quantitative yeast two-hybrid assays. Empty DNA-binding-domain vector was used as a control. Values represent -galactosidase units of representative experiments. Binding sites #1 and 2 produced similar high -galactosidase values upon interaction with APC-ARM when tested in the DNA-binding-domain vector (not shown).