Most yeast ribosomal protein genes are duplicated and their characterization has led to hypotheses regarding the existence of specialized ribosomes with different subunit composition or specifically-tailored functions. In yeast, ribosomal protein genes are generally duplicated and evidence has emerged that paralogs might have specific roles. Unlike yeast, most mammalian ribosomal proteins are thought to be encoded by a single gene copy, raising the possibility that heterogenous populations of ribosomes are unique to yeast. Here, we examine the roles of the mammalian Rpl22, finding that Rpl22−/− mice have only subtle phenotypes with no significant translation defects. We find that in the Rpl22−/− mouse there is a compensatory increase in Rpl22-like1 (Rpl22l1) expression and incorporation into ribosomes. Consistent with the hypothesis that either ribosomal protein can support translation, knockdown of Rpl22l1 impairs growth of cells lacking Rpl22. Mechanistically, Rpl22 regulates Rpl22l1 directly by binding to an internal hairpin structure and repressing its expression. We propose that ribosome specificity may exist in mammals, providing evidence that one ribosomal protein can influence composition of the ribosome by regulating its own paralog.

For almost five decades, antibiotics have been used successfully to control infectious diseases caused by bacterial pathogens. More recently, however, two-thirds of bacterial pathogens exhibit resistance and are continually evolving new resistance mechanisms against almost every clinically used antibiotic. Novel efforts are required for the development of new drugs or drug leads to combat these infectious diseases. A number of antibiotics target the bacterial aminoacyl-tRNA site (A site) of 16S ribosomal RNA (rRNA). Mutations in the A-site region are known to cause antibiotic resistance. In this study, a bacterial (E. coli) A-site rRNA model was chosen as a target to screen for peptide binders. Two heptapeptides, HPVHHYQ and LPLTPLP, were selected through M13 phage display. Both peptides display selective binding to the A-site 16S rRNA with on-bead fluorescence assays. Dissociation constants (K d s) of the amidated peptide HPVHHYQ-NH 2 to various A-site RNA constructs were determined by using enzymatic footprinting, electrospray ionization mass spectrometry (ESI-MS), and isothermal titration calorimetry (ITC) under a variety of buffer and solution conditions. HPVHHYQ-NH 2 exhibits moderate affinity for the A-site RNA, with an average K d value of 16 μM. In addition, enzymatic footprinting assays and competition ESI-MS with a known A-site binder (paromomycin) revealed that peptide binding occurs near the asymmetric bulge at positions U1495 and G1494 and leads to increased exposure of residues A1492 and A1493.It has been half a century since the first antibiotic penicillin was discovered and successfully applied to the treatment of infectious diseases; however, infectious diseases still remain the third-leading cause of death in the United States and the second-leading cause of death worldwide (1). Widespread and intensive use of antibiotics in hospitals and agriculture has led to significant levels of resistance (2,3). The emergence of antibiotic resistance, especially multidrug resistance, is a growing threat to human health (4). Therefore, a significant driving force exists for the development of new antimicrobial agents, especially those to combat multidrug-resistant pathogens.The majority of antibiotics used in the clinic target protein synthesis, which occurs at the core of the ribosome (5). High-resolution X-ray crystal structures of rRNA fragments, 30S and 50S subunits, and whole ribosomes, either free or complexed with antibiotics, have provided important information that will help in the design of new anti-infective compounds (6-10). † This work was supported by NIH grant AI061192. SUPPORTING INFORMATION AVAILABLEFigures S1-S4 show MALDI-TOF characterization of HPVHHYQ-NH 2 , ESI-MS data (salt dependence), and binding curve for RNase footprinting data (A1493). This material is available free of charge via the Internet at http://pubs.acs.org. NIH Public Access Author ManuscriptBiochemistry. Author manuscript; available in PMC 2010 September 8. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH...

Ribosomal RNA is the catalytic portion of ribosomes, and undergoes a variety of conformational changes during translation. Structural changes in ribosomal RNA can be facilitated by the presence of modified nucleotides. Helix 31 of bacterial 16S ribosomal RNA harbors two modified nucleotides, m 2 G966 and m 5 C967, that are highly conserved among bacteria, though the degree and nature of the modifications in this region are different in eukaryotes. Contacts between helix 31 and the P-site tRNA, initiation factors, and ribosomal proteins highlight the importance of this region in translation. In this work, a heptapeptide M13 phage-display library was screened for ligands that target the wild-type, naturally modified bacterial helix 31. Several peptides, including TYLPWPA, CVRPFAL, TLWDLIP, FVRPFPL, ATPLWLK, and DIRTQRE, were found to be prevalent after several rounds of screening. Several of the peptides exhibited moderate affinity (in the high nM to low µM range) to modified helix 31 in biophysical assays, including surface OPEN ACCESSMolecules 2011, 16 1212 plasmon resonance (SPR), and were also shown to bind 30S ribosomal subunits. These peptides also inhibited protein synthesis in cell-free translation assays.

Loop conformation: The loop of the RNA domain helix 69 (H69) was modified with the fluorescent analogue 2‐aminopurine (2AP), thus showing different conformational states under various conditions. The application of this model RNA reveals the unique impact of aminoglycoside neomycin, which differs from the effects of structurally related compounds paromomycin and gentamicin, on the H69 loop conformation in solution (see picture).