Polypyrimidine-tract-binding protein 1 (PTBP1), a 57-kDa RNA-binding protein that is also referred to as hnRNP1, has been implicated in various aspects of mRNA metabolism, including regulation of alternative splicing, internal ribosome-entry-site-driven translation, mRNA localization, and polyadenylation. Four tandem RNA-recognition-motif domains confer PTBP1 with a strong RNA-binding activity. PTBP1-mediated posttranscriptional regulation of gene expression has been reported for many genes, including CD154, insulin, vascular epithelial growth factor (VEGF), and human inducible nitric oxide synthase.