GCAP39 IS A NUCLEAR AND CYTOPLASMIC PROTEIN

gCap39 is a newly identified member of the Ca2+- and polyphosphoinosit ide-modulated gelsolin family of actin binding proteins which is diffe rent from gelsolin in several important respects: it caps filament end s, it does not sever filaments, it binds reversibly to actin, it is ph osphorylated in vivo, and it is also present in the nucleus. gCap39 an d gelsolin coexist in a variety of cells. To better understand the rol es of gCap39 and gelsolin, we have compared their relative amounts and intracellular distributions. We found that gCap39 is very abundant in macrophages (accounting for 0.6% of total macrophage proteins), and i s present in 12-fold molar excess to gelsolin. Both proteins are highl y induced during differentiation of the promyelocytic leukemia cell li ne into macrophages. gCap39 is less abundant in fibroblasts (0.04% tot al proteins) and is present in equal molar ratio to gelsolin. The two proteins are colocalized in the cytoplasm, but gCap39 is also found in the nucleus while gelsolin is not. Nuclear gCap39 redistributes throu ghout the cytoplasm during mitosis and is excluded from regions contai ning chromosomes. Our results demonstrate that gCap39 is a nuclear and cytoplasmic protein which has unique as well as common functions comp ared with gelsolin. (C) 1993 Wiley-Liss, Inc.