PTF1A (Pancreas transcription factor 1a; also p48 and bHLHA29) is a cell specific member of the bHLH family of proteins. Although its predicted MW is 41 kDa, a high ratio of Pro, Leu and Ala increases its MW to 48 kDa in SDS-PAGE. PTF1A forms a trimeric transcription factor complex with a p75 subunit (HEB, E2 or E47) and a p64 subunit (usually RBP-L). Within this complex, unfortunately termed PTF1, p48/PTF1A binds to a DNA E-box while p64 binds to a TC-box. This regulates the gene transcription of about 20 enzymes synthesized by pancreatic acinar cells. Human PTF1A is 328 amino acids (aa) in length. It contains one basic DNA binding HLH motif (aa 150-175) and a dimerization interface (aa 178-219). Over aa 1-92, human PTF1A shares 88% aa identity with mouse PTF1A.