Figure 3

In vitro growth and catastrophe of S. pombe MTs Plus end (red) and minus end (blue) growth rates versus tubulin concentration for purified S. pombe single (α1β) (A) and dual-isoform (α1β + α2β) tubulin (B), measured by DIC video microscopy at 25 °C. Tubulin concentrations were corrected for variable (minor) amounts of assembly-incompetent tubulin, quantitated using a MT pelleting assay. Dual isoform tubulin contains approx. 50:50 α1β and α2β tubulin heterodimers. Conditions: 100 mM K-PIPES, 1 mM MgSO₄, 2 mM EGTA, 1 mM DTT pH 6.9, no glycerol, 25 °C. Measured rate constants are summarized in Table 1. Similar data replotted from Walker et al.²⁷ for mammalian brain tubulin at 37 °C (C) Catastrophe rates versus MT growth rate for (D) α1β and (E) α1β + α2β tubulin. Error bars are SEM (A–C) and 95% CI (D,E).