NOVEL HOMOLOGS OF REPLICATION PROTEIN-A IN ARCHAEA - IMPLICATIONS FORTHE EVOLUTION OF SSDNA-BINDING PROTEINS

In Bacteria and Eukarya, ssDNA-binding proteins are central to most as pects of DNA metabolism. Until recently, however, no counterpart of an ssDNA-binding protein had been identified in the third domain of life , Archaea. Here, we report the discovery of a novel type of ssDNA-bind ing protein in the genomes of several archaeons. These proteins, in co ntrast to all known members of this protein family, possess four conse rved DNA-binding sites within a single polypeptide or, in one case, tw o polypeptides. This peculiar structural organization allows us to pro pose a model for the evolution of this class of proteins.