So each one of these dimers consists of 121212 of these regulatory chains. And this entire orange structure constitutes a single catalytic primer. So we have one, two, three of these orange subunits. Each one of these orange subunits is a catalytic chain. And three of these catalytic chains arranged in this triangular format make up that catalytic trimer. Now, because we're examining the structure from top to bottom, the other trimer is hiding beneath this trimer.