Binds to the plus end of microtubules and regulates the dynamics of the microtubule cytoskeleton. Promotes cytoplasmic microtubule nucleation and elongation. May be involved in spindle function by stabilizing microtubules and anchoring them at centrosomes. May play a role in cell migration. {ECO:0000269|PubMed:12388762; ECO:0000269|PubMed:16109370; ECO:0000269|PubMed:19632184; ECO:0000269|PubMed:21646404}.