Biological ion exchanger resins; IX. Isolation and partial identification of a potassium sensitive contractile-like...

A protein fraction with actin-like characteristics has been isolated from E. coli. The fraction (referred to as A-L fraction) undergoes reversible increases in molecular weight under the same catalytic conditions that polymerize actin, exhibits a distinct peak on SDS electrophoresis at the characteristic molecular weight for actin, depends primarily on potassium for its polymerization, and is not "polymerized" by sodium. A-L fraction in the monomeric form was eluted in the void volume of a Sepharose 6B column, suggesting a large Stoke's radius and a molecular weight in excess of 400,000. The fraction contained 30% RNA by weight that proved refractory to experimental efforts at removal.