Cloning and characterization of the proximal promoter region of the rat insulin-like growth factor I (IGF-I) receptor gene

We have isolated genomic clones that contain the promoter region of the rat IGF-I receptor gene. A unique transcriptional start site was suggested by the results of primer extension and RNase protection assays, which also defined a 940-base 5′-untranslated region. Despite the single start site, the proximal 415 base pairs of 5′-flanking region were devoid of TATA or CCAAT elements. The region surrounding the start site was, however, similar to a recently described "initiator" sequence that can direct specific transcription initiation in the absence of a TATA element. The 5′-flanking region was GC-rich and contained several possible SP1 sites, but also included potential ETF and AP-2 binding sites. The rat IGF-I receptor gene promoter region appears to have some sequences similar to both "housekeeping" and highly regulated promoters and may be an example of an intermediary class of regulatory region.