Structural analysis of Dis3l2, an exosome-independent exonuclease from Schizosaccharomyces pombe.

After deadenylation and decapping, cytoplasmic mRNA can be digested in two opposite directions: in the 5'-3' direction by Xrn1 or in the 3'-5' direction by the exosome complex. Recently, a novel 3'-5' RNA-decay pathway involving Dis3l2 has been described that differs from degradation by Xrn1 and the exosome. The product of the Schizosaccharomyces pombe gene SPAC2C4.07c was identified as a homologue of human Dis3l2. In this work, the 2.8 Å resolution X-ray crystal structure of S. pombe Dis3l2 (SpDis3l2) is reported, the conformation of which is obviously different from that in the homologous mouse Dis3l2-RNA complex. Fluorescence polarization assay experiments showed that RNB and S1 are the primary RNA-binding domains and that the CSDs (CSD1 and CSD2) play an indispensable role in the RNA-binding process of SpDis3l2. Taking the structure comparison and mutagenic experiments together, it can be inferred that the RNA-recognition pattern of SpDis3l2 resembles that of its mouse homologue rather than that of the Escherichia coli RNase II-RNA complex. Furthermore, a drastic conformation change could occur following the binding of the RNA substrate to SpDis3l2.