FGF2, also known as basic fibroblast growth factor (bFGF) and FGF-β, is a growth factor and signaling protein encoded by the FGF2 gene. It is synthesized primarily as a 155 amino acid polypeptide, resulting in an 18 kDa protein. However, there are four alternate start codons which provide N-terminal extensions of 41, 46, 55, or 133 amino acids, resulting in proteins of 22 kDa (196 aa total), 22.5 kDa (201 aa total), 24 kDa (210 aa total) and 34 kDa (288 aa total), respectively. Generally, the 155 aa/18 kDa low molecular weight (LMW) form is considered cytoplasmic and can be secreted from the cell, whereas the high molecular weight (HMW) forms are directed to the cell's nucleus. Fibroblast growth factor protein was first purified in 1975, but soon afterwards others using different conditions isolated basic FGF, Heparin-binding growth factor-2, and Endothelial cell growth factor-2. Gene sequencing revealed that this group was in fact the same FGF2 protein and that it was a member of a family of FGF proteins. FGF2 binds to and exerts effects via specific fibroblast growth factor receptor (FGFR) proteins which themselves constitute a family of closely related molecules.