Escherichia coli dinG gene encodes a putative DNA helicase related to a group of eukaryotic helicases including Rad3 protein.

DinG is an Escherichia coli DNA damage-inducible gene (1, 2). Sequence database searches (3, 4) revealed marginally significant similarities between the 637 amino acid DinG protein, yeast DNA helicases Chll, Rad3 and Rad 15, and the human helicase ERCC2. Remarkably, the similarities included some of the motifs conserved in the 'DExD/H' helicase superfamily (5). However, DinG sequence did not contain the A motif of the purine NTPbinding pattern, which is conserved in all helicases (5). This motif was found in the sequence of an unidentified (ORF) upstream of dinG. Thus the two ORFs may encode a single protein consisting of 752 instead of 637 amino acid residues. Extended variants of the seven motifs typical of the 'DExD/H' helicase superfamily and two other conserved motifs were identified in DinG and the related proteins (Fig. 1). Statistical significance of the alignment was confirmed by two independent methods and four sequence fingerprints that are unique to this set of (putative) helicases were derived (see legend to Fig. 1), indicating that they comprise a distinct group within the 'DExD/H' superfamily including both eukaryotic and prokaryotic members.