Running Title: Entropy-Variability Plots

Key-words: entropy-variability plots; globins; ras-like proteins; serine-proteases; recalcitrant residue positions; protein structure evolution 2 We introduce sequence entropy-variability plots as a method of analysing families of protein sequences, and demonstrate this for three well-known sequence families: globins, ras-like proteins, and serine-proteases. The location of an aligned residue position in the entropy versus variability plot correlates with structural characteristics, and with known facts about the roles of individual amino acids in the function of these proteins. The large numbers of known sequences in these families allowed us to introduce new filtering methods for variability patterns. The results are discussed in terms of a simple evolutionary model for functional proteins