Observation of Escherichia coli ribosomal proteins and their posttranslational modifications by mass spectrometry

Ribosomes from the K-12 strain of Escherichia coli were analyzed with good sensitivity and high mass accuracy using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Fifty-five of the 56 subunit proteins were observable. Mass spectral peak locations were consistent with previously reported post-translational modifications involving N-terminal methionine loss, methylation, thiomethylation, and acetylation for all but one case. The speed and accuracy of mass spectrometry make it a good candidate for phylogenetic studies of ribosomes and the observation of posttranslational modifications in other organisms.