The Sentin-N fragment interferes with synergistic growth acceleration and rescue induced by XMAP215^msps and EB1–Sentin. (A) GFP-Sentin-N (1–440 aa) and GFP-Sentin-ΔN (231–982 aa) recombinants used in this study. (B) Tracking of Sentin-N or Sentin-ΔN in the presence of EB1 or XMAP215^msps. (C) The Sentin-N fragment (600 nM) interfered with growth and rescue induced by 100 nM XMAP215^msps (XM), 400 nM EB1 (EB), and 200 nM full-length Sentin (Sen) at 15 µM tubulin. The mean values of each experiment are marked, and the mean values of all the experiments are indicated by black or red bars. For the growth rate, 21–38 events from 10–20 MTs were analyzed in each experiment (n = 2 experiments). None of 35 or 3 of 59 shrinking MTs showed rescue in the presence or absence of GFP-Sentin-N, respectively. (D) 200 nM Sentin-ΔN weakly accelerates growth and promotes rescue in the presence of EB1 and XMAP215^msps. Growth rate was 1.2 ± 0.2–fold at 15 µM tubulin (±SD; P < 0.04; n = 6 experiments, 11–43 events from 10–20 MTs were analyzed in each experiment). Rescue occurred more frequently with Sentin-ΔN (3 of 129 or 1 of 134 shrinking MTs showed rescue). (E) Model for the independent as well as cooperative action of XMAP215 polymerase and the EB1–Sentin duo that has growth acceleration and catastrophe promotion activities. N, N terminus; C, C terminus. Data from a single experiment are marked with the same shape. Bars: (horizontal) 5 µm; (vertical) 1 min.