Extended Data Figure 4: PA and PB2 structure and new inter-subunit interactions.
From: Structure of influenza A polymerase bound to the viral RNA promoter
a, Interactions of the PA-linker (green tube) with the outer surface of the fingers (pale cyan) and palm (pale salmon) domains of PB1. Contacts are mediated by both highly conserved hydrophobic residues (for example, PA residues Phe 205, Phe 211, Leu 214, Pro 220, Tyr 226, Phe 229, Tyr 232, Val 233, Ile 242, Leu 246, Met 249 and Val 253) and polar interactions (for example, PA Glu 203, Lys 230, Glu 243 and Lys 245 to PB1 Arg 162, Glu 331, His 465 and Asp 86, respectively). b, Transparent surface diagram showing the anchoring of the PA endonuclease domain (forest green) onto the PB1-Cter–PB2-Nter interface region (cyan/red) and its position relative to the PB2 cap-binding domain (orange). The nuclease helix α4 packs parallel to the penultimate PB1 helix α21 involving both hydrophobic (for example, PA Ile 86, Ile 90 and Ile 94 with PB1 Ser 720, Ile 724 and Ile 728, respectively) and polar interactions (for example, PA Glu 77 with PB1 Arg 727). Other contacts include the PB2 170-loop interacting with the same PA helix α4 in the vicinity of Trp 88. Also the endonuclease insertion (PA 70-loop, residues 67–74) packs on the first part of the last PB1 helix α22. The total buried surface area between the endonuclease and PB1/PB2 is 2,265 Å2.
