NF-M (Neurofilament medium polypeptide) is a neurofilament protein. Neurofilaments usually contain three intermediate filament proteins: L,Mouse, and H which are involved in the maintenance of neuronal caliber. Phosphorylation seems to play a major role in the functioning of the larger neurofilament polypeptides (NF-M and NF-H), the levels of phosphorylation being altered developmentally and coincident with a change in the neurofilament function. NF-M is phosphorylated in the head and rod regions by the PKC kinase PKN1, leading to inhibition of polymerization.