  We develop a simple optimization procedure for assigning binary values to the
amino acids. The binary values are determined by a maximization of the degree
of pattern conservation in groups of closely related protein sequences. The
maximization is carried out at fixed composition. For compositions
approximately corresponding to an equipartition of the residues, the optimal
encoding is found to be strongly correlated with hydrophobicity. The stability
of the procedure is demonstrated. Our calculations are based upon sequences in
the SWISS-PROT database.
