Bias toward +- configuration by separation distance. For each of four Pasteurellacaea, the height of the bar gives the total number of paired USS motifs separated by the given distance. The orange (lower) portion of the bar gives the number of pairs in the +- configuration. In H. influenzae, local peaks around approximately 8 and approximately 19-22 are due to the preservation of the extended USS motif. The distribution of distances is different for H. ducreyi, which has a peak of pairs (all in the +- configuration) at separations of 27 to 30, and the preference for the +- motif is not apparent until larger separation distances.