Evolution of the START domain among cellular organisms. A neighbor-joining phylogenetic tree was constructed based on the Poisson correction model and pairwise deletion algorithm (bootstrapped 2,000 replicates). START domains from multicellular eukaryotes are represented as follows: plant proteins from Arabidopsis are depicted by green lettering. Animal and Dictyostelium proteins are illustrated by white lettering on colored boxes as indicated in the key. START proteins from unicellular eukaryotic and prokaryotic species are classified according to genus and are shown by black lettering on colored boxes. Shaded areas indicate proteins that contain additional domains in combination with START: gray, plant-specific; yellow, animal-specific; orange, mammal-specific; lavender, Dictyostelium-specific. HD, homeodomain; ZLZ, leucine zipper-loop-zipper; ZIP, basic region leucine zipper; PH, pleckstrin homology; SAM, sterile alpha motif; RhoGAP, Rho-type GTPase-activating protein; 4HBT, 4-hydroxybenzoate thioesterase; Ser-rich, serine-rich region; DUF1336, domain of unknown function 1336. All other proteins (white background) contain no additional known domains besides START, but may contain additional sequence of unknown function and/or known function, such as transmembrane segments. Proteins less than 245 amino acids in length are designated START domain minimal proteins and are indicated by an asterisk. Accession codes for all proteins and coordinates of the START domains are listed in Tables 1,2,3,4.