Abstract
A cDNA encoding a putative RNA and/or DNA helicase has been isolated from Arabidopsis thaliana cDNA libraries. The cloned cDNA is 5166 bases long, and its largest open reading frame encodes 1538 amino acids. The central region of the predicted protein is homologous to a group of nucleic acid helicases from the DEAD/H family. However, the N- and C-terminal regions of the Arabidopsis cDNA product are distinct from these animal DEIH proteins. We have found that the C-terminal region contains three characteristic sequences: (i) two DNA-binding segments that form a probe helix (PH) involved in DNA recognition; (ii) an SV40-type nuclear localization signal; and (iii) 11 novel tandem-repeat sequences each consisting of about 28 amino acids. We have designated this cDNA as NIH (nuclear DEIH-boxhelicase). Functional character-ization of a recombinant fusion product containing the repeated region indicates that NIH may form homodimers, and that this is the active form in solution. Based on this information and the observation that the sequence homology is limited to the DEAH regions, we conclude that the biological roles of the plant helicase NIH differ from those of the animal DEIH family.
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