The intact lid complex is observed between 7,250 and 9,000 m/z, with the most intense peak at ≈8,000 m/z. Well-resolved charge states are observed, and the measured mass confirms the presence of all nine subunits. An overlapping charge series is detected and corresponds to a substoichiometric complex in which the Rpn6 subunit is absent (labeled with asterisks). A subcomplex of the lid gives rise to a signal in the range of 5,000–6,250 m/z.