Preparation, purification and properties of a crosslinked trimer of G-actin

Phenylenebismaleimide has been used to form crosslinks between actin monomers [Knight, P. and Offer, G. (1978) Biochem. J. 175, 1023-1032]. We have purified a trimer of actin monomers as well as a dimer and a mixture of higher molecular weight oligomers. The trimer is much more effective than the dimer in enhancing the rate of polymerization while higher oligomers do not appear to be any more effective than the trimer. A lag in the polymerization process, as measured fluorescence enhancement of trace pyrene-actin, still occurs in the presence of trimers serving as the nuclei, suggesting that the mechanism for polymerization is more complex than nucleation followed by elongation.