Non-neuronal microtubule-associated protein. Promotes microtubule assembly. Interacts with SEPTIN2; this interaction impedes tubulin-binding. Interacts with TRAF3IP1 (PubMed:26487268). Interacts with KNSTRN (By similarity). Recruitment to microtubule is inhibited by microtubules polyglutamylation. Testis, striated and cardiac muscle. Phosphorylated at serine residues in K-X-G-S motifs by MAP/microtubule affinity-regulating kinase (MARK1 or MARK2), causing detachment from microtubules, and their disassembly (By similarity). Phosphorylation on Ser-760 negatively regulates MAP4 activity to promote microtubule assembly. Isoform 4 is phosphorylated on Ser-333 and Ser-334 (By similarity). Truncated N-terminus. Extended N-terminus.