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A helicase in general is defined as “any of various enzymes that catalyze the unwinding and separation of double-stranded DNA or RNA during its replication”.〔Merriam-Webster. Merriam-Webster, n.d. Web. 15 Oct. 2014.〕 A helicase is more specifically considered a motor enzyme which receives its energy from nucleoside triphosphate hydrolysis to unwind double stranded nucleic acids.〔Kwong, Ann D., Govinda B. Rao, and Kuan-Teh Jeang. "Viral and Cellular RNA Helicases as Antiviral Targets." Nature.com. Nature Publishing Group, Oct. 2005. Web. 15 Oct. 2014.〕 In our case we are considering specifically RNA Helicase which is involved holistically in the metabolism of RNA which is found in all facets of life on earth.〔Jankowsky, Eckhard. RNA Helicases. Cambridge: Royal Society of Chemistry, 2010. Print.〕 RNA helicase (, ''CSFV NS3 helicase'', ''DBP2'', ''DbpA'', ''DDX17'', ''DDX25'', ''DDX3'', ''DDX3X'', ''DDX3Y'', ''DDX4'', ''DDX5'', ''DEAD-box protein DED1'', ''DEAD-box RNA helicase'', ''DEAD-box protein 2'', ''DEAH-box RNA helicase'', ''DED1'', ''Dex(H/D) RNA helicase'', ''EhDEAD1'', ''EhDEAD1 RNA helicase'', ''eIF4A helicase'', ''KOKV helicase'', ''Mtr4p'', ''nonstructural protein 3 helicase'', ''NPH-II'', ''RHA'', ''RNA helicase A'', ''RNA helicase DDX3'', ''RNA helicase Hera'', ''RNA-dependent ATPase'', ''TGBp1 NTPase/helicase domain'', ''VRH1'', ''GRTH/DDX25'') is an enzyme with system name ''ATP phosphohydrolase (RNA helix unwinding)''. This enzyme catalyses the following chemical reaction : ATP + H2O ADP + phosphate RNA helicases utilize the energy from ATP hydrolysis to unwind RNA. == Structure and Superfamilies == RNA helicases are split into two main categories based on their ability to form oligomeric structures. Of the six superfamilies (SFs) that exist, SFs 1 and 2 do not form rings, whereas SFs 3, 4, 5, and 6 do. The first two superfamilies, which are usually found in eukaryotes, are composed of a structurally conserved core that is usually surrounded by large N- and C- terminal domains that function as RNA and DNA binding domains, protein binding domains, and other molecular specific functions. The function of these domains is extremely significant in cellular interaction by increasing specificity of recruitment of proteins by using structurally specific complexes and sequences within families. These two helicases are also made up of at least 12 structural motifs are positioned in specific sequences that vary between families but are usually highly conserved within the same family.〔Jankowsky, Eckhard. "RNA Helicases at Work: Binding and Rearranging." Trends in Biochemical Sciences 36.1 (2011): 19-29. Web.〕 SFs 3 through 6 form hexameric rings, and are usually found in bacteria and viruses.〔 Proteins of the superfamilies 3 and 4 are most similar to each other. However, SF4 contains a packaging motor named P4 that plays a role of packaging the RNA into a phage by first unwinding the structure and translocating the information into capsids. SF5 contains a Bacterial Rho factor that works to regulate transcription termination as well as removing RNA polymerase. SF6 contains a structure that works similarly to the Bacterial Rho factor but is different structurally.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「RNA helicase」の詳細全文を読む スポンサード リンク
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