Fig. 5. Binding of mutant MAP4 forms to MTs. (A) WT-MAP4-expressing L^tk- cells before (ext) and after (H₁P) a single step of Taxol-dependent MT polymerization (Chapin et al., 1991) The Coomassie-stained electropherogram shows an enrichment of the tubulin band at 50 kDa in the H₁P fraction. (B) H₁P fractions from WT- and KK-MAP4 cells (AA- and EE-MAP4 are not shown) were eluted with 0-0.6 M NaCl, and the eluted material was assayed by western blotting with an antibody against human MAP4 (top two panels) and an antibody against endogenous mouse MAP4 (bottom panel). Essentially all MAP4 was released with 0.6 M NaCl. (C) Quantification of MAP4 eluted from crude MTs (H₁P) prepared from cells expressing transfected WT- and mutant MAP4 forms. Western blots such as those shown in Fig. 5B were scanned and the percentage of MAP4 released from H₁P fraction at each salt concentration is shown. The MAP4 in each eluted sample was quantified and normalized to the total MAP4 that was released by elution with 0.6 M NaCl. nd indicates that no MAP4 was detected in this sample; error bars show ±s.d.

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