Identification and initial characterization of a fourth leader exon and promoter of the human IGF-II gene.

Transcription of the human insulin-like growth factor II (IGF-II) gene is regulated by activation of multiple promoters which act in a tissue-specific and development-dependent manner. Previously, we have identified three different promoters, one of which is active in adult liver tissue only, whereas the other two are active in many fetal tissues and adult non-hepatic tissues. Here we report the identification of a fourth leader exon of the human IGF-II gene indicating the presence of a fourth promoter. Transcription from this promoter yields a 5.0 kb IGF-II mRNA species, which is detected in fetal liver and leiomyosarcoma tissue.