The saturation scan database for Ubv.2.1 (A) and Ubv.21.4 (B). The saturation scan database for Ubv.2.1 (A) and Ubv.21.4 (B). Following selection for binding to cognate USP, the percent occurrence of each amino acid was calculated after normalization for codon bias at each scanned position. The WT occurrences are boxed, and values are color-coded as follows: yellow, ≥10%; blue, ≤2%. Bits score were calculated as described in Materials and Methods. Isabel Leung et al. PNAS 2016;113:31:8705-8710 ©2016 by National Academy of Sciences