Toward Determining the Biological Function of a Novel Posttranslational Modification on the Ribosomal Protein S12.

The ribosome is the universal macromolecular machine that translates the mRNA transcript into polypeptides. Analytical techniques have facilitated characterization of this complex and the identification of various ribosomal protein isoforms that result from post-translational modifications (PTMs). Beta-methylthioaspartic acid was previously identified as a novel PTM at position 88 in the Escherichia coli ribosomal protein S12. D88 is universal among all S12 bacterial orthologs and mutations at this position are lethal. This unusual PTM has also been identified in the equivalent position of ribosomal protein S12 from three phylogenetically distinct bacteria suggesting, at the bacterial level, conservation of the modification. Our goal is to determine the biological function of this novel PTM by elucidating the enzymology of modification. We used homologous recombination to create an E. coli S12 gene that has two affinity tags at the C-terminus. To identify the modifying enzymes we utilized affinity purification to pull-down proteins that form interactions. We have used ID PAGE and LC/MS/MS to identify > 50 specifically interacting proteins. Several candidates, including putative methyl transferases, will be studied. [ABSTRACT FROM AUTHOR]