AF6-RBDGST (residues 1-141) protein.The amino terminus of Af6 was identified as the Rasbinding site. Additionally to the Ras-binding Af6 also bindsRap. ZO-1, a protein involved in the formation of tightjunctions, also binds to Af6 close to the amino terminusthereby competing with Ras binding. These data suggesta participation of Af6 in the regulation of cell-cell contacts via a Ras-modulated interaction with ZO-1. In contrast to the well characterized effectors Raf, RalGEF, andPI(3)kinase, Af6 is a protein with no enzymatic function.It seems to serve as a scaffolding component for proteincomplexes. This would represent a new type of Ras effector because Ras binding in this case does not lead to theactivation of the enzymatic activity of the effector.;