Post-translational processing of rat ribosomal proteins. Ubiquitous methylation of Lys22 within the zinc-finger motif of RL40 (carboxy-terminal extension protein 52) and tissue-specific methylation of Lys4 in RL29

Abstract

The complete amino acid sequences of rat and yeast (Saccharomyces cerevisiae) ribosomal proteins derived from precursors containing an N-terminal ubiquitin or ubiquitin-like sequence (C-terminal extension proteins or CEPs) were determined and investigated for any post-translational modifications by reverse-phase HPLC purification, direct amino acid sequence and mass spectrometric analyses. Covalent modifications were detected in the rat liver proteins RS27a (CEP-80), RL29, RL37 and RL40 (CEP-52), while RS30 (CEP), RL36a, RL39 and RL41 were unmodified. Heterogeneity of RS27a was due to C-terminal truncations, with Lys80 missing from about 20% of the liver RS27a population; C-terminal processi..