First of all, there is a good agreement between these results and available data on the structure and function of sequences examined. Secondly, there is a striking differences between results obtained by partial and ordinary correlation coefficients. It should be pointed firstly that the considered amino acid characteristics reflect physical inter-residue interactions as well as interactions between residues and protein environment. For the side chain volume these are sterical short-distance interactions. Isoelectric point could be associated with charge properties of amino acids.
Hydrophobicity characterizes interaction of residues with aqueous solution.
The last two properties for charged residues could be considered as related. One can see that matrices of the partial correlation coefficients are quite similar as obtained for hydrophobicity and isoelectric point, supposingly, due to a close nature of these properties. Next, there should be mentioned here a strong correlation in terms of hydrophobicity and isoelectric point quantities between positions flanking the DNA-binding region. The latter could be detected by the blocks of significant correlation coefficients in the left bottom parts of the respective matrices. They are designated as flanks in Figure 1b.