Alignment scores of 'noise' alignments. The alignment score averaged over all non-self 'noise' alignments for each protein is plotted against the size of the protein. All-alpha and all-beta classes are shown in red and green, respectively. These classes include alpha-helix bundles (e.g. d1f68a_) and beta-sandwiches (e.g. d1cida1), which produce high T-scores in the 100- to 200-residue range. The black points are for proteins other than all-alpha and all-beta classes.