Stu2p does not strongly require the COOH terminus of β-tubulin for binding to microtubules. (A) Mock- or subtilisin- digested microtubules analyzed by SDS-PAGE and Coomassie blue staining (left) or by Western blotting (right) using a monoclonal α-tubulin antibody (top) or a monoclonal β-tubulin antibody whose epitope lies within the COOH terminus of β-tubulin (bottom). (B, top) Mock- and subtilisin-digested microtubules visualized by immunofluorescence. Bar, 5 μm. (B, bottom) Increasing amounts of mock- or subtilisin-digested microtubules were incubated with 18 nM Stu2p and bound separated from unbound Stu2p by centrifugation. Equivalent amounts of the supernatants (S) and the pellets (P) were analyzed by SDS-PAGE and Western blotting using a polyclonal Stu2p antibody (top), a monoclonal α-tubulin antibody (middle), or a monoclonal β-tubulin antibody whose epitope lies within the COOH terminus of β-tubulin (bottom). (C) Plot showing the percentage of Stu2p bound to mock- or subtilisin-digested microtubules at different microtubule concentrations.