CLONING AND ANALYSIS OF AN HMG GENE FROM THE LAMPREY LAMPETRA-FLUVIATILIS - GENE DUPLICATION IN VERTEBRATE EVOLUTION

Evolution has shaped the organisation of vertebrate genomes, including the human genome. To shed further light on genome history, we have cl oned and analysed an HMG gene from lamprey, representing one of the ea rliest vertebrate lineages. Genes of the HMG1/2 family encode chromoso mal proteins that bind DNA in a non-sequence-specific manner, and have been implicated in a variety of cellular processes dependent on chrom atin structure. They are characterised by two copies of a conserved mo tif, the HMG box, followed by an acidic C-terminal region. We report h ere the cloning of a cDNA clone from the river lamprey Lampetra fluvia tilis containing a gene with two HMG boxes and an acidic tail; we desi gnate this gene LfHMG1. Molecular phylogenetic analysis shows that LfH MG1 is descended from a gene ancestral io mammalian HMG1 and HMG2. Thi s implies that there was a duplication event in the HMG1/2 gene family , that occurred after the divergence of the jawed and jawless fishes, 450 million years ago. This conclusion supports and refines the hypoth esis that there was a period of extensive gene duplication early in ve rtebrate evolution. We also show that the HMG1/2 family originated bef ore the protostomes and deuterostomes diverged, over 525 million years ago.