Chart 1. Decay of E-values in PSI-BLAST results using human ABCG proteins as query. A minor decay occurs after the first 4 sequences (ABCG1 and ABCG4 of human and mouse), followed by ABCG2, ABCG5 and ABCG8 of human and mouse. Then, sequences homologous to Drosophila White, and Abcg3 are found. Beginning with sequence 19, the plant WBC and PDR families are featured, starting with WBC14 from Arabidopsis, followed by many members of these families forming a rather slow descending slope, until at sequence 80 (NAP12, Arabidopsis) the point of decay is reached. This extends up to sequence 83 (Q18900, Caenorhabditis elegans). A second plateau is reached at sequence 84 (MALK, Escherichia coli), followed by a plethora of Escherichia coli proteins and human proteins of other subfamilies (starting with ABCAs, which are known as the closest human homologs to the ABCG transporter proteins).