Thus it remains open if IQGAP1 influences the activity of mDia1 directly like it does for NWASP. In contrast to the Arp 2/3 complex, formins nucleate the formation of unbranched actin filaments. FH2 domains lack structural similarity to actin but can bind actin monomers with very weak affinity. The FH2 dimer nucleates filament assembly by interacting directly with and stabilizing actin polymerization intermediates (dimers and trimers). A formin dimer remains constantly bound to the plus end of an actin filament despite ongoing polymerization. One formin of a dimer dissociates from the barbed end to take the next step while the second formin of the dimer remains bound. Thus the formin dimer processively adds actin monomers to the barbed end and are constantly present at the barbed end of an actin filament (processive capping). The FH1 domain recruits actin monomers through profilin binding, but it does not promote nucleation. Studies demonstrated that FH2 domains protect the rapidly elongating barbed ends of filaments from the vast molar excesses of actin capping proteins. The precise mechanisms of actin filament nucleation remains an area of active investigation. The rate of FH2 movement while elongation on an actin filament matches the rate of actin subunit addition, which can exceed 100 subunits per second. Profilin as a ubiquitous actin-binding protein is associated with most actin monomers in cells. Interactions between profilin-actin with the FH1 domain can accelerate the elongation at the FH2-capped barbed ends. The formin homology protein mDia1 is a Rho GTPase effector protein, which appears to be universally present in eukaryotic cells and participates in:   Stress fibers are acto-myosin structures, which are important for establishment of cellular tension and thus traction to move a cell ahead; the later is mediated via cell adhesions. Stress fibers are bundles of about 20 actin filaments linked via non-muscle myosin II. "In vitro" studies showed that mDia1 assembled stress fibers downstream of Rho. Live-cell imaging analysis revealed that mDia1 indeed assembles stress fibers, which are connected at one of their ends to focal adhesions, where actin polymerization occurs.