Conservation of Microtubule Associated Proteins ISOLATION AND CHARACTERIZATION OF ,r AND THE HIGH MOLECULAR WEIGHT MICROTUBULE ASSOCIATED PROTEIN FROM CHICKEN BRAIN AND FROM MOUSE FIBROBLASTS AND COMPARISON TO THE CORRESPONDING MAMMALIAN BRAIN PROTEINS*

Using ability to stimulate tubulin assembly as an assay, we have purified a chicken brain associated protein under conditions identical to those used to isolate porcine brain 7 protein. Chicken brain T has a molecular weight, sedimentation coefficient, and amino acid composition very similar to porcine r. Both r proteins are microheterogeneous and yield very similar and characteristic one-dimensional peptide maps. We have also isolated 7 and a high molecular weight protein from simian virus 40-transformed 3T3 cells by copolymerization of labeled cellular proteins with carrier hog brain microtubules. The simian virus 3T3 cell proteins co-electrophorese with the corresponding hog brain associated proteins and yield peptide maps which are indistinguishable from the hog protein patterns. These findings confirm the presence of 7 and a high molecular weight microtubule associated protein from a nonneuronal source and demonstrate that both are present in a single cell type, as originally suggested by immunofluorescent localization with antibodies against the hog brain proteins. Moreover, the similarities of the T polypeptides from the three sources studied (hog brain, chicken brain, and mouse fibroblast) imply that T is a widely distributed and conserved microtubule protein. The similarities between the high molecular weight associated proteins from hog brain and mouse fibroblast suggest that they, too, are widely distributed.