A PUTATIVE BETA-TUBULIN PHOSPHATE-BINDING MOTIF IS INVOLVED IN LATERAL MICROTUBULE PROTOFILAMENT INTERACTIONS

We have investigated the role of a putative GTP-binding beta-tubulin m otif in microtubule polymerization. A peptide containing residues 126- 142 of the beta-tubulin subunit (peptide G) was synthesised and an ant ibody against it raised. Peptide G prevents the binding of GTP to tubu lin and also microtubule polymerization but not the formation of vinbl astine-induced tubulin spirals, suggesting that it may prevent lateral but not longitudinal tubulin-tubulin interactions. The antibody to pe ptide G shows little reaction with the interphase microtubule network, mitotic spindles or midbody of cultured cells, whereas it clearly rea cts with vinblastine-induced paracrystals. These results suggest that this putative phosphate-binding site present in beta-tubulin could be involved in the lateral tubulin-tubulin interactions along the microtu bule structure.