Unique 3′‐untranslated sequence of insulin‐like growth factor‐I isolated from human placenta

A cDNA clone of 525 bp corresponding to the 3′-untranslated region of insulin-like growth factor-I was isolated from a human placenta library. The sequence of this clone extended 200 nucleotides downstream from the previously reported 3′-end of IGF-IA cDNA, indicating the existence of IGF-IA transcripts having an even larger 3′-untranslated region. By using this clone for RNA transfer blot hybridization, it was shown that this longer 3′-untranslated region is included in the 7.5- and 5.0-kb transcripts, but not in the 1.1- and 0.9-kb transcripts. It is also apparent that transcripts bearing the extended 3′-untranslated sequence are highly expressed in human placenta.