The very nature of RNA molecule,which separates it from DNA and protein molecules,is sequence-specific recognition through three types of base pairs:G-C,A-U,and G-U pairs.These pairs form RNAs secondary structure,which encodes dynamic and regulatory information about the cell.While DNA nucleotides mostly form a double helix by forming hydrogen bonds between complementary bases,RNA nucleotides are free to interact with each other to form complex structures because of the singlestrand nature of RNA.Early studies revealed that many canonical noncoding RNAs (ncRNAs),such as rRNA,tRNA,group Ⅰ/Ⅱ introns,and riboswitches,are folded into well-defined secondary and tertiary structures.For long noncoding RNAs (IncRNAs),although their sequences are usually poorly conserved,their structural domains are likely organized into scaffolds that interact with other molecules (Mercer and Mattick,2013).The local RNA structure context also contributes to the binding specificity of particular types of RNA-binding proteins (Hu et al.,2016).