Regulation Mechanism of H. sapiens Tutase II

Abstract

TUT2 is a human non-canonical poly(A) polymerase which polyadenylates, monoadenylates, and monouridylates mRNA and miRNA in the cytoplasm (Chung et al., 2016). GLD2, the C. elegans homolog of TUT2 requires a partner protein, GLD3, for catalytic activity. OAS1, a structural homolog of GLD2, requires double-stranded RNA (dsRNA) induced conformational change to become a catalytically active oligoadenylate synthetase. Comparison of the OAS1•dsRNA and GLD2•GLD3 co-crystal structures revealed that dsRNA and GLD3 occupy equivalent sites on OAS1 and GLD2. The current model based on C. elegans is that GLD3 binding to GLD2 creates a positively charged RNA binding site (Nakel et al., 2015). However, based on the OAS1•dsRNA structure, we propose an alternative model in which GLD3 induces a conformational change in GLD2. To investigate these models, we used human TUT2 \(\Delta\)1-155, which is equivalent to the crystallized C. elegans GLD2. Surprisingly, we found that this construct is constitutively catalytically active and can polyadenylate RNA in isolation. Additionally, we found that at a concentration of 1.4 \(\mu\)M, a human BICC1 homologous fragment to GLD3 does not affect the activity of TUT2. Our findings indicate the nucleotidyl transferase domain in TUT2 alone is sufficient for polyadenylation.