Figure 8. Paralogous instances of mobile elements show selective pressures matching transcription factor binding preferences.

We hypothesized that when a particular region of the mobile element is repeatedly exapted, it may be used to perform the same function in paralogous instances. We collected sequences in the human genome representing families of paralogs, that all originated from the same bases of a mobile element insertion. We used MEME [63] to define a motif for this family that represents the selective pressure acting on these insertions after their exaptation by the host. In 6 cases this motif has a significant match to the binding preference of transcription factors (p-values are corrected for multiple tests). These results are consistent with mobile element consensus sequences spreading functional, or near-functional, transcription factor binding sites throughout the genome, which are then exapted by the host. A more detailed analysis of one of these matches is shown in Figure 9.