Figure 7. N⁶‐methylation of an adenine in human SRP, at a trans Hoogsteen‐sugar A·G base pair that mediates a tertiary contact.

1. A schematic showing the secondary structure of human SRP. Below is shown methylated sequence, and its equivalent in the Alu element BC200. Both have been shown to be N⁶‐methylated at the adenine boxed in red.
2. The tertiary contact between helices 31 (green, containing the A·G pairs) and helix 1 (yellow) in the Alu domain of SRP, PDB 5AOX 58. The A·G pairs both form trans Hoogsteen‐sugar base pairs with the adenine bases directed into the minor groove of the H1 helix. A107 makes hydrogen bonding contacts between the two helices.