title: Two domains of superfamily I helicases may exist as separate proteins.
abstract: DNA and RNA helicases of superfamily I are characterized by seven conserved motifs. The five N-terminal motifs are separated from the two C-terminal ones by a spacer that is highly variable in both sequence and length, suggesting the existence of two distinct domains. Using computer methods for protein sequence analysis, we show that PhoH, an ATP-binding protein that is conserved in Escherichia coli and Mycobacterium leprae, is homologous to the putative N-terminal domain of the helicases, whereas the putative E. coli protein YjhR is homologous to the C-terminal domain. These findings suggest that the N-and C-terminal domains of superfamily I helicases have distinct activities, with only the N-terminal domain having the ATPase activity. It is speculated that PhoH and YjhR have evolved from helicases through deletion of the portions of the helicase genes coding for the C- and N-terminal domain, respectively.
authors.affiliation: National Center for Biotechnology Information, National Library of Medicine, NIH, Bethesda, Maryland 20894, USA. koonin@ncbi.nlm.nih.gov
authors.forename: E V
authors.initials: EV
authors.lastname: Koonin
authors.forename: K E
authors.initials: KE
authors.lastname: Rudd
mesh_terms: D000595:Amino Acid Sequence; D017124:Conserved Sequence; D004265:DNA Helicases / Q000737:chemistry*; D004926:Escherichia coli / Q000737:chemistry; D008969:Molecular Sequence Data; D009166:Mycobacterium leprae / Q000737:chemistry; D020365:RNA Helicases; D012316:RNA Nucleotidyltransferases / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid
chemical_list: D012316:RNA Nucleotidyltransferases; D004265:DNA Helicases; D020365:RNA Helicases