IDENTIFICATION OF ACTIN-BINDING PROTEINS FROM SEA-URCHIN EGGS BY F-ACTIN AFFINITY COLUMN CHROMATOGRAPHY

Novel F-actin binding proteins of sea urchin eggs were searched for in order to study regulation of the actin cytoskeleton during fertilizat ion and cell division, An extract of unfertilized eggs was analyzed by F-actin column chromatography. Several previously characterized F-act in-modulating proteins such as spectrin, myosin, and fascin bound to t he column. The eluates from the column also contained proteins having apparent molecular weights of 225K, 150K, 70K, 60K, 45K, 40K, 38K, 36K , 34K, 20K, and 15K, which were thought to be novel cytoskeletal prote ins judging from their molecular weights and non-reactivity 60 antibod ies against previously characterized F-actin-modulating proteins. Most of the proteins in the F-actin column eluates co-sedimented with F-ac tin, Partial amino acid sequences of the peptides derived from the 45K and 40K proteins showed that these proteins are homologous to Arp3 an d Arp2 subfamilies of actin-related proteins, respectively, The 150K p rotein seemed to be an unconventional myosin, that belongs to myosin V I subfamily. Amino acid sequences of two fragments from the 60K protei n showed homology to that of coronin. The 150K protein was localized b y immunofluorescence microscopy to the cleavage furrows in both whole cell sample and isolated cortex of dividing eggs. The 70K protein was uniformly localized in the cortical layer in the whole egg, but weak s taining of the cleavage furrow region with the antiserum was observed in the isolated cortex, The 60K protein was localized to both the bulk cortical layer and the cleavage furrow, but the modes of localization were different.