CHARACTERIZATION OF THE HUMAN SMALL-RIBOSOMAL-SUBUNIT PROTEINS BY N-TERMINAL AND INTERNAL SEQUENCING, AND MASS-SPECTROMETRY

Reverse-phase HPLC was used to fractionate 40S ribosomal proteins from human placenta, Application of a C-4 reverse-phase column allowed us to obtain 27 well-resolved peaks. The protein composition of each chro matographic fraction was established by two-dimensional polyacrylamide gel electrophoresis and N-terminal sequencing. N-terminally blocked p roteins were cleaved with endoproteinase Lys-C, and suitable peptides were sequenced. All sequences were compared with these of ribosomal pr oteins available from data bases. This allowed us to identify all prot eins from the 40S human ribosomal subunit in the HPLC elution profile. By matrix-assisted laser-desorption ionization mass spectrometry the masses of the 40S proteins were determined and checked for the presenc e of post-translational modifications. For several proteins difference s to the deduced sequences and the calculated masses were found to be due to post-translational modifications.