An atypical Iron-Responsive Element (IRE) within crayfish ferritin mRNA and an Iron Regulatory Protein 1 (IRP1)-like protein from crayfish hepatopancreas

A putative crayfish iron-responsive element (IRE) is present in the 5'-untr anslated region of the crayfish ferritin mRNA. The putative crayfish IRE is in a cap-proximal position and shares most of the structural features of t he consensus IRE, but the RNA stem-loop structure contains a bulge of a gua nine instead of a cytosine at the expected position, so far thought to be a hallmark of IREs. By using an electromobility shift assay this IRE was sho wn to specifically bind purified recombinant human iron regulatory protein 1 (IRP1) as well as a factor(s) present in a homogenate of crayfish hepatop ancreas, likely to be a crayfish IRP1 homologue. With mutations in the cray fish IRE, the affinity of IRP to IRE was drastically decreased. A cDNA(2) e ncoding an IRP1-like protein was cloned from the hepatopancreas of crayfish . This protein has sequence similarities to IRP, and contains all the activ e-site residues of aconitase, two putative RNA-binding regions and a putati ve contact site between RNA and IRP. These results show that a crayfish IRE , lacking the bulged C, can bind IRP1 in vitro and that an IRP1-like protei n present in crayfish hepatopancreas may have both aconitase and RNA-bindin g activities. (C) 1999 Elsevier Science Ltd. All rights reserved.