H2AC20 and breast cancer: C-tails of different H2A variants have been shown to affect nucleosome structure and dynamics (e.g., H2A variants with short C-tails, such as H2A.B, H2A.P, and H2A.L are known to form nucleosomes with unwrapped DNA [28,50]), play important roles as sites of additional post-translational modifications (e.g., H2A.X S139 is a known phosphorylation site activated due to DNA damage response [51], H2A.Z.1 K101me2 contributes to the development of breast cancer [52], or interaction partners with other chromatin proteins (e.g., H1 [49,53].