Bacillus subtilis aconitase is an RNA-binding protein

The aconitase protein of Bacillus sabtilis was able to bind specifically to sequences resembling the iron response elements (IREs) found in eukaryotic mRNAs, The sequences bound include the rabbit ferritin IRE and IRE-like se quences in the B: subtilis operons that encode the major cytochrome oxidase and an iron uptake system. IRE binding activity was affected by the availa bility of iron both in vivo and in vitro . In eukaryotic cells, aconitase-l ike proteins regulate translation and stability of iron metabolism mRNAs in response to iron availability, A mutant strain of B. subtilis that produce s an enzymatically inactive aconitase that was still able to bind RNA sporu lated 40 x more efficiently than did an aconitase null mutant, suggesting t hat a nonenzymatic activity of aconitase is important for sporulation. The results support the idea that bacterial aconitases, like their eukaryotic h omologs, are bifunctional proteins, showing aconitase activity in the prese nce of iron and RNA binding activity when cells are iron-deprived.