Table 1.

Structures, functions and interactions of important residues identified within Drosophila XRN1 (PACMAN) [69]

Structure	Characteristics	Residues	Interactions/functions
Catalytic domain		1-674
	Mg2+ binding/active site	Asp35, Asp86, Glu177, Asp205, Asp207, Asp288	Co-ordination of two Mg2+ ions and water molecules for RNA hydrolysis
	Tower domain	533-542	Allows only exonuclease activity in the active site and interacts with the Winged helix domain
	Stacking residues	His41, Trp540	Organizes first three nucleotides into a π-π stack; His41 required for processive degradation
	Basic pocket	Lys93, Gln97, Arg100, Arg101	5′-phosphate binding excludes capped RNA and maintains 5′-nucleotide position for cleavage
	α1-helix and Trp540 loop	4-13, 533-542	Steric barrier at entrance to active site to exclude double stranded RNA and facilitate duplex unwinding
β-barrel domain	Similarity to PAZ/Tudor domains	674-779	Interacts with catalytic domain for stability
β-barrel domain	Similarity to KOW/SH3 domains	800-850, 1031-1045
α-helical domain	Winged helix domain	851-1026	Interacts with Tower domain
SH3-like domain	Lacks canonical SH3 residues for proline rich binding	1046-1140	Interacts with N-terminal for stability