Functional analysis of multiple promoters of the rat insulin-like factor II gene

We have characterized the multiple promoters of the rat insulin-like growth factor II (rIGFII) gene by in vivo transient expression assay using a series of deletion mutant templates. Among the four promoters (P1, P2, P3 and P6), two (P2 and P3) showed relatively strong promoter activities compared with the other two. One of the four promoters, P2, was further characterized by gel band-shift and footprinting analysis using HeLa cell nuclear extract, showing two retarded bands and at least one protected sequence stretch. The results indicated that P2 has a very simple structure like P3, and consists of no more than 141 base-pairs (bp) including a TATA box and two GC core hexanucleotides. Promoter strength shown by in vivo transient expression in different cell types failed to explain the differential employment of P2 and P3 in these cells, suggesting the involvement of other regulatory mechanisms that might operate only in the native state.