HSP70‐related 65 kDa protein of beet yellows closterovirus is a microtubule‐binding protein

Abstract
Beet yellows virus (BYV) genome encodes a 65 kDa protein homologous to the HSP70 family of cellular heat‐shock proteins (Agranovsky, A.A., Boyko, V.P., Karasev, A.V., Koonin, E.V. and Dolja, V.V. (1991) J. Mol. Biol. 217, 603–610). The respective gene was cloned and expressed in vitro yielding a product of the expected size (p65). This product was found to bind to the purified microtubules with a binding constant of 4 × 10−7 M. The binding of p65 was stimulated if ATP presented in the translation mixture was hydrolyzed by apyrase. Removal of the short C‐terminal domains of α‐ and β‐tubulin by subtilisin digestion abolished the binding, demonstrating its specificity. The possible role of p65 association with microtubules in the movement of virus within and/or between plant cells is proposed.