Jeff Pitt <japitt at thor.herl.epa.gov> wrote
>Does anyone know how far upstream, in a gene's promotor region, a dioxin
>responsive element (DRE) can be and be functional? Or does the DRE need
>to be near other promotor and enhancer regions?
The classical definition of an enhancer is a DNA element that can bind a
transcription factor(s) and, independent of distance and orientation,
functions to promote transcription of a gene. However, the "independent of
distance" part actually has some physical limitations (generally <10 Kbp).
Dioxin response elements (DREs) usually appear to be within a few kb of the
basal promoter of the genes they regulate (e.g. CYP1A1, studied by J.
Whitlock and others). I am not aware of any methodical study to define the
maximal distance of their effects (anybody else?). Due to the relatively
simple sequence of the core DRE (TNGCGTG), you would expect them to be
present ~ every 4e6 bp (~1/4096 bp, frequently occurring in many plasmid
sequences). Whether a putative DRE is functional must be experimentally
determined by i) demonstrating that the adjacent gene(s) are dioxin
responsive, and ii) demonstrating that deletion or mutation of the DRE
reduces or eliminates the responsiveness to dioxin.
Dr. Charles A. Miller, rellim at mailhost.tcs.tulane.edu
Bionet.toxicology news group:
Dept. Environmental Health Sciences, SL29
Center for Bioenvironmental Research
Tulane Univ. School of Public Health and Tropical Medicine
1430 Tulane Ave.
New Orleans, LA 70112