REGULATION OF IRON-METABOLISM IN THE SANGUIVORE LAMPREY LAMPETRA-FLUVIATILIS - MOLECULAR-CLONING OF 2 FERRITIN SUBUNITS AND 2 IRON-REGULATORY PROTEINS (IRP) REVEALS EVOLUTIONARY CONSERVATION OF THE IRON-REGULATORY ELEMENT (IRE) IRP REGULATORY SYSTEM/

Two ferritin cDNAs were cloned from the liver and spinal cord of the s anguivore lamprey Lampetra fluviatilis, an extant representative of th e ancient agnathan (jawless) stage in vertebrate evolution. The deduce d proteins of 20.2 kDa (H-subunit) and 20.1 kDa (M-subunit) display 73 % sequence identity, and both contain the ferroxidase center characte ristic of animal H-ferritin. A highly conserved iron-responsive elemen t (IRE) was identified in the 5' untranslated region of lamprey H-ferr itin. Lamprey ferritin IRE forms a specific complex with crude lamprey and rat liver extracts, and with recombinant human iron-regulatory pr otein (IRP-1) in an electrophoretic mobility shift assay. Furthermore, lamprey ferritin IRE competes with labeled human ferritin IRE for bin ding to IRP in lamprey and mammalian extracts. Two liver cDNA sequence s encoding 323 residues and 101 residues of two genetically distinct l amprey IRP were amplified by PCR. Lamprey IRP-1 and IRP-2, which are 7 2% identical, display about 74% sequence identity to their presumed ho mologues in mammals. Northern blot analysis shows that two IRP transcr ipts of 3.6 kb and 5.8 kb are expressed in lamprey liver. Given the an cient lineage of lampreys, the results indicate that the IRE/IRP regul atory system has remained highly conserved during the evolution of ver tebrates.