S 1 Q-incorporation into stem loop RNA Q-incorporation by human TGT into tRNA Asp , a tRNA Asp anticodon stem loop or the Y32U33G34U35 stem loop construct used for crystallization. The incorporation reactions contained either 4 µM tRNA or 5 µM stem loop RNA, 1 mM queuine and 0.5 to 10 µM TGT and were incubated for 1 h (tRNA Asp ) to 2.5 h (stem loops) at 37 °C. Reaction samples were separated on a boronate affinity electrophoresis gel, which causes retardation of queuine-containing RNA through interaction via its cis-diol. S 2 Electron density of the RNA stem loop An mFo-DFc omit map of the RNA stem loop (chain C) contoured at σ = 3.0 is shown as grey mesh. (A): Overview of the hTGT-RNA structural model. (B): Close-up of the helical stem focusing on nucleotides 29-31.
Angiogenin is an unusual member of the RNase A family and is of great interest in multiple pathological contexts. Although it has been assigned various regulatory roles, its core catalytic function is that of an RNA endonuclease. However, its catalytic efficiency is comparatively low and this has been linked to a unique C-terminal helix which partially blocks its RNA-binding site. Assuming that binding to its RNA substrate could trigger a conformational rearrangement, much speculation has arisen on the topic of the interaction of angiogenin with RNA. To date, no structural data on angiogenin–RNA interactions have been available. Here, the structure of angiogenin bound to a double-stranded RNA duplex is reported. The RNA does not reach the active site of angiogenin and no structural arrangement of the C-terminal domain is observed. However, angiogenin forms a previously unobserved crystallographic dimer that makes several backbone interactions with the major and minor grooves of the RNA double helix.
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