The article explains what is actin and claims that the synthesis of actin fibers, which are essential for cell division, is ruled by informational field, not by mechanical forces as other authors think. Since only nonlinear field can imprint information, the informational field needs to be nonlinear electromagnetic field (NEMF). The lifelong studies of NEMFs by the author helped her to understand that informational NEMF must be involved in the activation of actin. The synthesis of actin starts when the informational field says that it is time an old cell to be replaced by a new cell.