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. So if we take this structure and flip it this way, we're going to see this on top. And the other trimer is basically found on the bottom. So we have a total of two catalytic primers and three of these dimers on the sides.