Characterization of Escherichia coli 50S ribosomal protein L31

The published C-terminal sequence of Escherichia coli 50S ribosomal protein L31,...RFNK (Brosius, J. (1978) Biochemistry 17, 501-508), differs from th at predicted by the gene sequence,...RFNKRFNIPGSK (GenBank accession no. X7 8541). This discrepancy might be due to post-translational processing of th e protein. To examine this possibility, we have isolated L31 from E. coli s train MRE600 and sequenced the C-terminal tryptic peptide. We find the sequ ence to be FBIPGSK. Size comparisons of L31 from several E. coli strains de monstrate that all are identical in size to the protein isolated from MRE60 0 and larger than the previously described protein, indicating that...RFNKR FNIPGSK represents the true C-terminus of L31. In addition, we show that th e failure to identify L31 in many ribosome preparations is probably due to the protein's loose association with the ribosome and its ability to form v arious intramolecular disulfide bonds, leading to L31 forms with distinct m obilities in gels. (C) 1999 Federation of European Microbiological Societie s. Published by Elsevier Science B.V. All rights reserved.