Fig. 7

Models for the function and dynamics of retrotransposons in T. monococcum centromeres. A Schematic simplified model of the RLG_Cereba integrase complex. The CR domain specifically binds directly to CENH3 in nucleosomes, thereby ensuring selective insertion into functional centromeres. The CR domain is connected through a  tether/linker to the integrase core enzyme, directing the insertion of the double-stranded DNA (dsDNA) to a nearby loop in the chromatin fiber. B Sequence turnover and maintenance of centromeres. Step 1: The nucleosomes in and around centromeres are shown simplified by colored circles. The autonomous RLG_Cereba retrotransposons (blue boxes) replicate and insert copies of themselves into centromeres. Additionally, they also cross-mobilize RLG_Quinta retrotransposons. New RLG_Cereba and RLG_Quinta copies are inserted near nucleosomes that contain CENH3 histone variants. Step 2: The presence of QuinCent sequence motifs (see Fig. 6) in RLG_Quinta promotes recruitment of new CENH3 histone variants through unknown mechanisms. Step 3: Over time, CENH3 variants in distal parts are lost, thereby maintaining size the functional centromere. Additional CENH3 may be deposited in the functional centromere over time