Playing with LEGO® made of DNA (keep playing ... almost over)

The fun in LEGO® is putting the bricks together. You can do it with DNA bricks too! DNA bricks must be equipped with "cohesive ends" that bind one brick to another in a specific and automatic way.

Cohesive ends are short stretches of complementary sequences: when they meet they make double helixes bridging two bricks and thus letting them assemble automatically.

Now design the ends (the purple segments in the diagram) to assemble 3 DNA bricks. The goals is the structure shown below. Choose the right options with the selectors.

schematized as: