Interaction in vitro; proteins produced as a recombinant fusion proteins in bacterial system.

One Act5C molecule binds one spir WH2 domain.

The A205E and P244K mutations render Act5C protein completely non-polymerizable.

spir protein expressed and purified from bacteria.

Act5C protein expressed and purified in baculovirus-Sf9 cell system.

The spir WH2 repeats act as a scaffold to bring Act5C subunits into a longitudinal arrangement that nucleates actin polymerization.