Direct Fe2+ sensing by iron-responsive messenger RNA:repressor complexes weakens binding.
Fe(2+) is now shown to weaken binding between ferritin and mitochondrial aconitase messenger RNA noncoding regulatory structures ((iron-responsive element) (IRE)-RNAs) and the regulatory proteins (IRPs), which adds a direct role of iron to regulation that can complement the well known regulatory protein modification and degradative pathways related to iron-induced mRNA translation. We observe that the K(d) value increases 17-fold in 5'-untranslated region IRE-RNA:repressor complexes; Fe(2+), is studied in the absence of O(2). Other metal ions, Mn(2+) and Mg(2+) have similar effects to Fe(2+) but the required Mg(2+) concentration is 100 times greater than for Fe(2+) or Mn(2+). Metal ions also weaken ethidium bromide binding to IRE-RNA with no effect on IRP fluorescence, using Mn(2+) as an O(2)-resistant surrogate for Fe(2+), indicating that metal ions bound IRE-RNA but not IRP: Fe(2+) decreases IRP repressor complex stability of ferritin IRE-RNA 5-10 times compared with 2-5 times for mitochondrial aconitase IRE-RNA, over the same concentration range, suggesting that differences among IRE-RNA structures contribute to the differences in the iron responses observed in vivo. The results show the IRE-RNA:repressor complex literally responds to Fe(2+), selectively for each IRE-mRNA.
Khan
Mateen A
MA
Department of Chemistry, Hunter College, City University of New York, New York, New York 10065, USA.
Walden
William E
WE
Goss
Dixie J
DJ
Theil
Elizabeth C
EC
D000818:Animals; D007501:Iron / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics*; D011817:Rabbits; D011898:Ranidae; D012045:Regulatory Sequences, Nucleic Acid; D012097:Repressor Proteins / Q000378:metabolism*; D020218:Response Elements / Q000235:genetics*
D012333:RNA, Messenger; D012097:Repressor Proteins; D008345:Manganese; D007501:Iron; D008274:Magnesium