THE SAM DOMAIN OF POLYHOMEOTIC, RAE28, AND SCM MEDIATES SPECIFIC INTERACTIONS THROUGH CONSERVED RESIDUES

The SAM (sterile alpha motif) domain is a 65- to 70-amino acid sequenc e found in many diverse proteins whose functions range from signal tra nsduction io transcriptional repression, We show that the SAM domain o f the Drosophila Polycomb group protein, polyhomeotic (ph), is capable of binding io itself in vitro. We test a number of near relatives of the ph SAM domain from fruit fly mouse, and yeast and show that all ar e capable of self-binding. Heterologous interactions are seen among a subset of SAM domains, including ph, Scm, and RAE28. Several conserved amino acid residues were mutated in the ph SAM domain, and the effect s on self-binding and heterologous association were demonstrated. [33, [41, and 162 are shown io be important determinants of the binding in terface, while W1 and G50 are likely essential for the structure of th e domain. (C) 1998 Wiley-Liss, Inc.