Serves as the scaffold for the assembly of a complex that links key players in the nucleation and termination of actin filament assembly with a ubiquitous barbed end-directed motor. This complex is composed of at least capping proteins (acpA and acpB), the Arp2/3 complex, type I myosins (myoB and myoC) and carmil. It has at least a modest ability to activate Arp2/3-dependent actin nucleation. CARMIL localizes along with the Arp2/3 complex, myoB, and myoC in the leading edge of cells and it plays a significant role in the structure and function of these actin-rich cellular extensions. Interacts (via PXXP domains) with myoB and myoC (via SH3 domain). Interacts (via N-terminus) with the capping proteins acpA and acpB. Interacts (via the region between the LRR domain and COOH-terminal proline-rich domain) with the seven member Arp2/3 complex (arpB/Arp2, arpC/Arp3, arcA/p41-arc, arcB/p34-arc, arcC/p21-arc, arcD/p20-arc and arcE/p16-arc). Found in dynamic actin-rich cellular extensions, including the leading edge of cells undergoing chemotactic migration, and dorsal, cup-like, macropinocytic extensions. Down-regulated by Pseudomonas aeruginosa, PAO1 strain and PA14 strain infection. Cells exhibit a striking defect in the formation of dorsal, cup-like, macropinocytic structures, a concomitant reduction in the rate of fluid phase pinocytosis, a significant decrease in the efficiency of chemotactic aggregation, and a decrease in cellular F-actin content. Belongs to the CARMIL family.