Actin-binding proteins (Abps) are generally classified according to their hz vitro and ha vivo effects on actin organization. One class binds to globular actin (G-actin) and shifts the G~--+ filamentous actin (F-actin) equilibrium in favour of the unpotymerized form causing depolymerization of the filaments. A second class of Abps is able to bind to either end of the filament and hinder further addition of monomers to these ends. These proteins are called F-actin capping proteins. Some of them have the ability to break actin filaments through a non-proteolytic mechanism and are referred to as F-actin severing proteins. The third group interacts laterally with actin filaments and ca. n stabilize, protect or interconnect the filaments. Some of them link the filaments with other cytoskeletal elements. Abps have been reviewed by Stossel et aL (Anntt Rev Cell Biol 1985, 1: 353-402) and by Pollard and Cooper (Annu Rev Biocbem 1986,