Figure 1

Human IGF-1 alternative splicing and encoded propeptides. The igf-1 gene gives rise to multiple mRNA transcripts by alternative splicing. The different IGF-1 mRNA transcripts encode several precursor proteins, which differ by the length of the aminoterminal (signal) peptide and the structure of the extension peptide (E-peptide) on the carboxy-terminal end. The mature IGF-1 peptide results from posttranslational cleavage of all precursor polypeptides, by which the signal and the E-peptide are removed. Exons 5 and 6 encode distinct portions of the E-peptide (called the E-domain) with alternative carboxy-terminal sequences of the extension peptide. The IGF-1Ec splice variant is an exon 4-5-6 variant that produces an E-peptide, termed Ec-peptide. The synthetic MGF E-peptide that comprises the last 24 C-terminal amino acids (aa) of Ec-peptide is shown.