Similarity score of sequences to a motif is predictive of frequency.

<p>Similarity of each chromosomal position to the discovered (parent) motif was calculated as a stand in for relative affinity using a linear nucleotide position matching algorithm (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042761#s2" target="_blank"><b>methods</b></a>). All positions were ranked and the mean similarity score of groups of 100 with serially lower affinity scores were plotted against the mean frequency of those positions. The x-axis left margin is 5 because a bit score of 0 (the statistical similarity between random sequences) should be 5.25 for the parent motif under investigation. The rightmost edge of the x-axis represents the discovered highest similarity (11.25) of a single region of the chromosome to the discovered parent motif, representing a best fit and thus maximal similarity of the set. (<b>a</b>) The similarity scores in the initial (unselected) library did not produce a statistically significant trend when subjected to regression analysis. (<b>b–d</b>) The similarity scores from sequential sequence cycles of afSELEX-seq against their corresponding frequencies revealed exponential regression models (black lines) with r² values all over 0.90.