Structural features important for the RNA chaperone activity of zinc finger-containing glycine-rich RNA-binding proteins from wheat (Triticum avestivum) and rice (Oryza sativa).

Despite the increase in understanding of RNA chaperone activity of zinc finger-containing glycine-rich RNA-binding proteins (RZs) during the cold adaptation process, the structural features relevant to the RNA chaperone activity of RZs still largely remain to be established. To investigate the structural determinants important for the RNA chaperone activity of RZs, domain-swapping and deletion analyses was carried out to assess the contribution of the N-terminal zinc finger RNA-recognition motif (RRM) domain and the C-terminal glycine-rich region of wheat (Triticum avestivum) and rice (Oryza sativa) RZs to RNA chaperone activity. Although the amino acid sequence similarity among wheat TaRZ2, wheat TaRZ3, and rice OsRZ1 was high, only TaRZ2 had RNA chaperone activity as evidenced by complementation ability in cold-sensitive Escherichia coli mutant cell under cold stress and in vivo and in vitro nucleic acid-melting activity. Domain-swapping and deletion analysis demonstrated that the overall folding of RZs governed by the N-terminal RRM domain and the C-terminal glycine-rich region, as well as the size of the disordered C-terminal glycine-rich region, are crucial for the RNA chaperone activity of RZs. Collectively, these results indicate that a specific modular arrangement of RRM domain and the disordered C-terminal region determines the RNA chaperone activity of RZs in cells.