The Proximal Promoter Region
Within a promoter, the fundamental component is the ~100-bp basal promoter that provides an assembly platform for the RNA polymerase II initiation complex. These modules vary among genes and can contain a TATA box 25–30 bp upstream of the transcription start site, an initiator element lacking the TATA sequence or a null basal promoter containing neither. All of the studied insulin promoters contain a TATA box. However, the chicken promoter is distinct from the others in that at least two isoforms can be transcribed from alternative initiation sites. In E1.5 chicken embryo pancreas, the single insulin gene is also transcribed from an upstream secondary promoter to yield an mRNA with an additional 32-bp leader sequence. Inspection of available chicken genome sequence reveals that this alternative start site must be the product of a secondary basal transcription complex, as the transcript includes the genomic sequence from immediately upstream of the TATA box (25 bp upstream from the start of transcription) to the beginning of exon 1. The lack of another TATA box within the promoter and the presence of a C at –1 and an A at +1 of the longer transcript suggest that transcription is most likely established by an initiator element.
Diabetes. 2006;55(12):3201-3213. © 2006 American Diabetes Association, Inc.
Cite this: Comparative Analysis of Insulin Gene Promoters: Implications for Diabetes Research - Medscape - Dec 01, 2006.