Fig. 3.

Tandem mass spectra of eukaryotic ribosomes. Tandem mass spectra of ions of the stalk complexes isolated in the quadrupole from 60 S subunits of eukaryotic ribosomes in 1 m ammonium acetate, pH 7.5 are shown. The stripped complexes at m/z higher than the isolated charge state show pentamers, in all cases, from which one protein has dissociated (stripped pentamers). This reveals their universal pentameric nature. At lower m/z values individual, highly charged proteins released from the complex are observed. Insets show the 7+ charge states of P1 and P2 with magnesium adducts and, in the case of ribosomes from rabbit, phosphorylation of the P1 and P2 proteins.