Purification of a multiprotein complex containing centrosomal proteins from the Drosophila embryo by chromatography with low-affinity polyclonal antibodies.

A 190-kDa centrosomal protein interacts with microtubules when Drosophila embryo extracts are passed over microtubule-affinity columns. We have obtained a partial cDNA clone that encodes this protein. Using a fusion protein produced from the clone, we have developed a novel immunoaffinity chromatography procedure that allows both the 190-kDa protein and a complex of proteins that associates with it to be isolated in in a single step. For this procedure, the fusion protein is used as an antigen to prepare rabbit polyclonal antibodies, and those antibodies that recognize the 190-kDa protein with low affinity are selectively purified on a column containing immobilized antigen. These low-affinity antibodies are then used to construct an immunoaffinity column. When Drosophila embryo extracts are passed over this column, the 190-kDa protein is quantitatively retained and can be eluted in nearly pure form under nondenaturing conditions with 1.5 M MgCl2, pH 7.6. The immunoaffinity column is washed with 1.0 M KCl just before the elution with 1.5 M MgCl2. This wash elutes 10 major proteins, as well as a number of minor ones. We present evidence that these KCl-eluted proteins represent additional centrosomal components that interact with the 190-kDa protein to form a multiprotein complex within the cell.