Complete characterization of the human IGF-I nucleotide sequence isolated from a newly constructed adult liver cDNA library

A full-size cDNA sequence coding for insulin-like growth factor I (IGF-I) was isolated from a human liver library. For the construction of this bank, a new method was developed which anneals dG-tailed cDNA with a synthetic adaptor 5'-AATTCCCCCCCCCCC-3' followed by ligation into the EcoRI site of a lambda immunity-insertion vector. Based on the sequence analysis of the complete IGF-I messenger we concluded that the protein is synthesized as a precursor containing a signal peptide of 22 or 25 amino acid residues. In addition, the sequence extended in the 3'-direction and showed the presence of multiple polyadenylation sites in the IGF-I message.