Representative architectures of Mas domain-containing proteins. Membrane topology predictions for the 66 Mas proteins listed in Table 4 indicated that the conserved domain was located on the extracellular side of the cytoplasmic membrane. The Mas domain was predicted to remain anchored in the majority of proteins (A), but cleaved in eight (B). Three transmembrane segments were identified in seven proteins and four of these were classified as RDD domains (C, D). Five proteins contained an N-terminal coiled-coil region (E), and one, a serine-threonine protein kinase domain (STPK; F).