Background: Helicases play crucial role in almost all the nucleic acid metabolism including replication, repair, recombination, transcription, translation, ribosome biogenesis and splicing and these processes regulate plant growth and development. It is suggested that helicases play essential roles in stabilizing growth in plants under stress because their presence in the stress-induced ORFs has been identified. Moreover in a recent study we have reported that SUV3 helicase from Oryza sativa (OsSUV3) functions in salinity stress tolerance in transgenic rice by improving the antioxidant machinery. SUV3 helicase has been identified and characterized from yeast and human systems but the properties and functions of plant SUV3 are poorly understood.
Results: In this study, the purification and extensive characterization of recombinant OsSUV3 protein (67 kDa) is presented. OsSUV3 binds to DNA and RNA and exhibits DNA as well as RNA-dependent ATPase activities. It also contains the characteristic DNA and RNA helicase activity. OsSUV3 can use mainly ATP or dATP as energy source for the unwinding activity and it cannot unwind the blunt-end duplex DNA substrate. It is interesting to note that OsSUV3 unwinds DNA in both the 5'-3' and 3'-5 directions and thus its activity is bipolar in vitro. The Km values of OsSUV3 are 0.51 nM and 0.95 nM for DNA helicase and RNA helicase, respectively.
Conclusions: This study is the first direct evidence to show the bipolar DNA helicase activity of OsSUV3 protein. The unique properties of OsSUV3 including its dual helicase activity imply that it could be a multifunctional protein involved in biologically significant process of DNA and RNA metabolisms. These results should make significant contribution towards better understanding of SUV3 protein in plants.