Figure 5

Model for the origin of the P1-rw1077 enhancer region by non-homologous end-joining. The bottom bar illustrates the P1-rw1077 end adjacent to a P1-wr repeat. The top bar represents schematically a full length P1-wr repeat flanked by partial P1-wr copies on both sides (drawn as dark grey, tan and light grey rectangles, respectively). The green rectangle indicates part of a sequence that was proven to have enhancer function in P1-rr. A model demonstrating the progression from a P1-wr sequence to a unique P1-rw1077 enhancer structure is briefly outlined. A DNA double-strand break was initiated by the excision of a Mu-like transposable element (purple triangle) and the resulting gap was expanded by exonuclease activity. DNA repair was accomplished by non-homologous end-joining as implied by the presence of filler DNA (yellow rectangle). The filler DNA AACCTATGT is derived from a sequence close to the deletion end point (see light grey balloon). The neighboring 725 bp (purple rectangle) originated from the excised MULE. The light blue rectangles specify sequences that are duplicated due to the deletion of less than a full-length P1-wr repeat. Note that the terminal P1-wr copy only contains the 5' end and is similar to the 3' large repeat of P1-rr and P1-rw, which does not have any gene function and therefore should be considered as intergenic region. Due to the unknown origin of P1-rw1077 and P1-rr, we use the designation P1-wr also for P1-wr- like alleles that share regulatory and coding regions with P1-wr[B73].