Mass spectrometry of CRP proteins. (A) CRP proteins were purified from three isogenic strains carrying pRH31 by immuno-precipitation using anti-CRP agarose beads. Purified proteins were separated on a 15% SDS-polyacrylamide gel electrophoresis followed by Coomassie Brilliant Blue staining. The band I, II, and III corresponding to the full-length, truncated and DD-tagged CRP proteins were cut out from the gel, treated with lysyl endopeptidase, and subjected to mass spectrometry analysis. The expected peptide sequences and molecular weights of the C-terminal fragments of proteins are shown. The arginine rare codons are shown in bold, and the tag sequences derived from tmRNA-DD are underlined. (B) MALDI-TOF spectrum for the DD-tagged CRP protein purified from ssrADD cells. The specific signals corresponding to the C-terminal fragments are shown by arrows, and the signals matched to the other CRP fragments are shown by asterisks.
