Turning RacGAP into a RhoGAP

We already knew the players—MgcRacGAP, Aurora B, and RhoA—and that knocking out any one of them caused failure of cytokinesis; but it wasn't clear how they were connected. Now, it appears that Aurora B phosphorylates the GAP domain of MgcRacGAP, allowing it to turn its GAP activity toward RhoA, according to data from Yukinori Minoshima, Toshiyuki Kawashima, Toshio Kitamura (University of Tokyo, Tokyo, Japan), and colleagues.

When they first isolated MgcRacGAP, the group found that most of its activity was directed toward Rac1 and Cdc42, but there were hints—although inconsistent ones—that it also had activity toward Rho proteins. In the new work, Kitamura and colleagues found that, late in mitosis, Aurora B, RhoA, and MgcRacGAP congregate at the midbody, where Aurora B phosphorylates a serine in the GAP domain of MgcRacGAP. The phosphorylated GAP protein...