Figure 4. Identification of the direct interaction between lncRNA ZFAS1 and DDX21 protein. (A) Bioinformatics online database predicting the specific binding sequence and domain of lncRNA ZFAS1 secondary structure and DDX21 protein. (B) CLIP database illustrating the critical motif of lncRNA ZFAS1 (AAGC/CAGA) interacting with DDX21; MOE multi-functional docking platform showing the specific docking sites between ZFAS1 tertiary structure and DDX21 protein. (C) The DDX21 was determined the cellular localization and expression levels after knocking down or overexpressing lncRNA ZFAS1 in SW620 and SW480 cells by IF assays (C). Scale bar = 50μm. (D) The protein expression levels of DDX21 were determined by translation inhibition assay. (E) Co-localization of lncRNA ZFAS1 and DDX21 protein detected by the combination of ISH and IF assays in SW620 and SW480 cells. Scale bar = 5μm. (G and F) RNA pull-down followed by western blot showing the direct interaction of the ZFAS1-WT, ZFAS1-Mut, and antisense RNA probes with DDX21 protein after lncRNA ZFAS1 knockdown.