GFAP, a class-III intermediate filament, is a cell-specific marker that, during the development of the central nervous system, distinguishes astrocytes from other glial cells. Interacts with SYNM. Interacts with PSEN1 (via N-terminus). Associated with intermediate filaments. Brain; isoform 2 expressed at 20-fold lower level than isoform 1. Phosphorylated by PKN1. Belongs to the intermediate filament family.