Location of the actin-binding site on mammalian B2 and B1-subunits and in yeast B compared with an Archaean B-subunit that does not bind microfilaments. Identical colors indicate high conservation. The position of the minimal actin binding domain is indicated by the blue transparent square. As depicted, the C-terminus of the actin binding domain is highly conserved between B2, B1, and yeast, but the N-terminal portion is less well conserved. Part of the sequence that makes up the actin binding domain is missing in the Archaean, and the rest is only modestly conserved. The sequence of the “profilin-like domain,” which is in the red conserved domain, is provided below. Mutation of the phenylalanine to a glycine is sufficient to reduce the binding affinity for actin about 10-fold.