To date, eight closely related homologs of the Escherichia coli UmuC protein have been identified. All of these homologs appear to play critical roles in damage-inducible mutagenesis in enterobacteriaceae. Recently, a distantly related UmuC-homolog, DinB, has also been identified in E. coli. Using the polymerase chain reaction together with degenerate primers designed against conserved regions found in UmuC-like proteins, we have identified a new member of the UmuC-superfamily in the archeon Sulfolobus solfataricus. This new homolog shows high sequence similarity to DinB and a lower level of similarity to UmuC. As a consequence, we have called this new gene dbh (dinB homolog). Analysis of approximately 2.7 kb DNA encompassing the dbh region revealed several open reading frames (orfs). One, encoding a putative ribokinase, was located immediately upstream of dbh. This orf overlaps the dbh gene by 4 bp suggesting that both proteins might be coordinately expressed. Further upstream of the ribokinase-dbh locus was another orf encoding a potential ATPase homologous to two uncharacterized S. cerevisiae proteins (YD9346.02c and SC38KCXVI_20) and another E. coli DNA repair protein, RuvB. While this is the first report of a UmuC-like homolog in an archeon, we detected additional homologs using protein sequence comparisons in Gram-positive bacteria, cyanobacteria, and among potential human EST products, indicating that UmuC-related proteins comprise a ubiquitous superfamily of proteins probably involved in DNA repair and mutagenesis.