(a) Each oval represents one residues in Lem27 (top) and ubiquitin (bottom), the contact site described in Figure 6 are also indicated. Color codes: positively charged residues (H, His; K, Lys; R, Arg) are colored in blue; negatively charged residues (D, Asp; E, Glu) are colored in red; the neutral residues (S, Ser; T, Thr; N, Asn; Q, Gln) are colored in green; aliphatic residues (A, Ala; V, Val; L, Leu; I, Ile; M, Met) are colored in grey; aromatic residues(F, Phe; Y, Tyr; W, Trp) are colored in magenta, Pro and Gly are colored in orange; cysteine is colored in yellow. (b) Mutagenesis analysis of Lem27 residues involved in interacting with ubiquitin. A series of 14 mutants in the indicated residues were constructed in Lem271-417. Each protein was purified and assayed for the ability to cleave K6-linked diubiquitin. Results shown were the percentage of the activity wild-type protein. Data shown are mean ±s.e. from three independent experiments.