pI(Cln) and cytosolic F-actin constitute a heteromeric complex with a constant molecular mass in rat skeletal muscles

To elucidate the function of pI(Cln), its localization in subcellular organ ellae was investigated. A specific polyclonal anti-pI(Cln) antibody detecte d the soluble 38-kDa pI(CIn) exclusively in the cytosols of rat heart, lung , liver, spleen, skeletal muscle, testis, and brain, but not rat kidney, pI (Cln)-associated proteins in skeletal muscle were also analyzed. Native-gra dient PAGE showed a single 340-kDa protein band reactive to anti-pI(Cln) an tibody. This band also stained with anti-actin antibody. Two-dimensional PA GE and immunoprecipitation analysis indicated that all of the pI(Cln) was p resent in association with actin of a constant length: the molecular ratio of pI(Cln) to actin was roughly 1:7. In addition, all actin in the cytosol fractions was found in association with pI(Cln). These results suggest the possibility that skeletal muscle pI(Cln) controls the length of cytosolic F -actin.