Effects of cytochalasin and phalloidin on actin

C YTOCHALASINS and phalloidins are two groups of small, naturally occurring organic molecules that bind to actin and alter its polymerization. They have been widely used to study the role of actin in biological processes and as models for actin-binding proteins. Functionally, cytochalasins resemble capping proteins, which block an end of actin filaments, nucleate polymerization, and shorten filaments. No known actin-binding protein stabilizes actin filaments as phalloidin does, but such proteins may have been missed. Cytochalasin and phalloidin have also helped to elucidate fundamental aspects of actin polymerization. This review briefly summarizes older studies and concentrates on recent v~rk on the mechanisms of action of cytochalasin and phalloidin.