Structure-based sequence alignment between H‑BRCT domains of Sir4 (top) and Dbf4 (PDB 3QBZ, bottom). Secondary structural elements present in the Sir4 H‑BRCT crystal structure are displayed above the Sir4 sequence (α, α-helix; β, β-strand; η, 3.10 helix). Dbf4 residues strongly contributing to Rad53 FHA1 binding are highlighted with black (interface I) and blue (interface II) asterisks. The elongated loop connecting helix α3 and strand β4 in Sir4 H‑BRCT is labelled with an orange bar and the Tyr198 (Dbf4) to Lys1064 (Sir4) exchange is highlighted with colored arrows. 