carried in bloodstream by steroid binding protein (binds with low affinity)
freely diffuse (only target tissues respond)
upon termination: modified then cleared from the body
Steroid Hormone Receptors
when bind ligand: unmask DNA binding site, complex with response elements on DNA
highly conserved structural subunits—all have four regions in this order (N-terminal to C-terminal):
(1) regulatory region (fine tune activity)
(2) DNA binding region (zinc finger)
(3) hinge (proline-rich region—flex protein)
(4) steroid binding (where steroid binds)
of the four subunits listed above, DNA binding region is most conserved among different receptors, steroid binding region somewhat conserved, others not conserved
very high affinity for ligand (10-10 M) and high specificity
effect determined by amount of time bound
c-erb-A is an oncogene—so steroid hormone receptors can cause malignancy
Steroid Response Elements (Enhancer)
-200 to –70 in 5’ flanking sequence
when bound by receptor, target protein mRNA is transcribed
occluded in some tissues (tissue specificity of gene activation)