Regulation of tubulin polypeptides and microtubule function: Rki1p interacts with the beta-tubulin binding protein Rbl2p

Genetic analysis of microtubule functions in the yeast Saccharomyces cerevi siae suggests that cells manage the levels and activities of the tubulin po lypeptides. These reactions may be involved in protein folding, formation o f the heterodimer, and maintenance of the appropriate balance between alpha - and beta-tubulin. One protein involved in these functions is Rb12p, which forms a complex with beta-tubulin. Here we describe the identification of a novel yeast gene, RkI1, that interacts genetically with RBL2. Deletion of rki1 causes conditional defects in microtubule assembly and cell growth. R ki1p can be isolated in a complex containing Rbl2p. The results support the existence of cellular mechanisms for regulating microtubule function throu gh the tubulin polypeptides.