Dear Editor,DEAD-box proteins,which are named after the strictly conserved amino acid sequence Asp-Glu-Ala-Asp,were first identified as a distinct family in the late 1980s when alignments based on eight homologues of the yeast elF4A highlighted the presence of several conserved motifs (Linder et al.,1989).DEAD-box proteins are widely distributed in different life forms,ranging from bacteria to human and constitute the largest RNA helicase family (Jiang et al.,2016).They are involved in many aspects of RNA metabolism,such as splicing,mRNA export,transcriptional and translational regulation,ribosome biogenesis and RNA decay (Rocak and Linder,2004).The core of DEAD-box proteins is organized into two major domains.Domain 1 (DEAD domain) consists of motifs Q,I (Walker A,P-loop),Ⅱ (Walker B,DEAD-box),la,GG,Ⅰb and Ⅲ,whereas domain 2 (Helicase domain) consists of motifs Ⅳ,Ⅴ and Ⅵ.Different motifs are involved in nucleotide binding (Q,Ⅰ and Ⅱ),RNA binding (la,Ⅰb,Ⅳ and Ⅴ) and ATP hydrolysis (Ⅲ and possibly Ⅵ).Compared with the two conserved domains,the N-and C-terminal regions are variable and divergent.Their functions are not fully characterized,but they are thought to confer their own specificity on different proteins (Hogbom et al.,2007).