W250 Nucleic Acids Research, 2007, Vol. 35, Web Server issue Figure 3. (A) A screenshot of the output of the oPOSSUM Human SSA analysis, with TFBS proﬁles ranked by Z-score. The arrows allow the user to sort and re-order the results by Fisher score, TF name, TF class, TF supergroup or TF proﬁle information content (IC). Each TF name links to a pop-up window displaying the TFBS proﬁle information. (B) Pop-up window displaying genes that contain a particular TFBS (in this case, MEF2A; partial list shown), as well as the promoter coordinates associated with each gene, and the motif locations and scores. Sites in overlapping alternative promoters are highlighted for emphasis. Such sites are only counted once in the statistical analysis. site proﬁles. The output for oPOSSUM CSA is similar, providing (i) a ranked list of over-represented TFBS class combinations, and (ii) a list of the most signiﬁcant TFBS combinations (found in the set of expanded top-ranked class combinations). Based on the underlying assumption of the statistics employed that DNA sequences are randomly generated, there is little reason to accept the calculated scores as accurate reﬂections of signiﬁcance. Instead, as suggested in the original published description of the oPOSSUM