Biochemical characterization of isolated CHO cell mitotic spindles: identification of calmodulin-binding proteins

Mitotic spindles were isolated from Chinese hamster ovary (CHO) cells and examined morphologically and biochemically. The isolated spindles were observed to be intact structures containing associated chromosomes and were surrounded by a cage of vimentin-containing filaments. Two-dimensional gel electrophoresis of isolated spindles versus whole cell homogenates indicated that isolated spindles were free from significant cytoplasmic contamination and contained tubulin, actin, vimentin and an 80 X 10(3) Mr quadrapeptide as their major protein constituents. Five calmodulin-binding proteins with molecular weights of 200, 160, 130, 60 and 52 (X 10(3] Mr were identified within isolated spindles. These calmodulin-binding proteins may be involved in regulating microtubule organization and depolymerization during karyokinesis.