DIFFERENT ASSEMBLY PROPERTIES OF COD, BOVINE, AND RAT-BRAIN MICROTUBULES

Assembly properties of cod, bovine, and rat brain microtubules were co mpared. Estramustine phosphate, heparin, poly-L-aspartic acid, as well as NaCl, inhibited the assembly and disassembled both bovine and rat microtubules by inhibition of the binding between tubulin and MAPs. Th e assembly of cod brain microtubules was in contrast only marginally a ffected by these agents, in spite of a release of the MAPs. The result s suggest that cod tubulin has a high intrinsic ability to assemble. T his was confirmed by studies on phosphocellulose-purified cod tubulin, since the critical concentration for assembly was independent of the presence or absence of MAPs. The results show therefore that cod brain tubulin has, in contrast to bovine and rat brain tubulins, a high pro pensity to assemble under conditions which normally require the presen ce of MAPs. Even if cod MAPs, which have an unusual protein compositio n, were not needed for the assembly of cod microtubules, they were abl e to induce assembly of bovine brain tubulin. Both cod and bovine MAPs bound to cod microtubules, and bovine MAP1 and MAP2 bound to, and sub stituted at least the 400 kDa cod protein. This suggests that the tubu lin-binding sites and the assembly-stimulatory ability of MAPs are com mon properties of MAPs from different species. independent of the tubu lin assembly propensity.