Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.2.1.23 (beta-galactosidase)
 14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

During protein synthesis on the ribosome, the growing peptide is linked covalently to a transfer RNA. With a certain probability this peptidyl-tRNA dissociates from the ribosome, whereupon it becomes susceptible to hydrolysis catalyzed by peptidyl-tRNA hydrolase. When placed at nonpermissive temperatures, mutant (pthts) Escherichia coli that are temperature-sensitive for the hydrolase will accumulate peptidyl-tRNA, suffer inhibition of protein synthesis, and eventually die. Treating cells with chloramphenicol before raising the temperature prevents cell death but erythromycin, other macrolides, and lincosamide antibiotics all enhance cell death. Accumulation of peptidyl-tRNA by pthts cells at high temperatures is blocked by chloramphenicol but enhanced by macrolides and lincosamides. The data are most consistent with macrolide and lincosamide antibiotics having as their primary mechanism of inhibition the stimulation of peptidyl-tRNA dissociation from the ribosome. Rather than blocking peptide bond formation or peptidyl-tRNA translocation from the A- to the P-site of the ribosome, these antibiotics allow the synthesis of small peptides which dissociate as peptidyl-tRNAs before being completed. Low doses of erythromycin and lincomycin stimulate preferentially the dissociation of peptidyl-tRNAs that are erroneous. Errors in proteins can be assessed by the time necessary to inactivate beta-galactosidase at > 55 degrees C. Whether erroneous peptidyl-tRNAs are induced by treating E. coli with streptomycin or ethanol, or by starving for an amino acid, the shortened time to inactivate beta-galactosidase is counteracted if the cells are simultaneously treated with erythromycin or lincomycin. In contrast, errors in beta-galactosidase caused by synthesis in the presence of canavanine, an arginine analogue, cannot be counteracted by the simultaneous presence of erythromycin. This result rules out any effect of the drug on post-translational mechanisms of error correction.
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PMID:Mechanism of inhibition of protein synthesis by macrolide and lincosamide antibiotics. 885 69

The expression of minigenes in bacteria inhibits protein synthesis and cell growth. Presumably, the translating ribosomes, harboring the peptides as peptidyl-tRNAs, pause at the last sense codon of the minigene directed mRNAs. Eventually, the peptidyl-tRNAs drop off and, under limiting activity of peptidyl-tRNA hydrolase, accumulate in the cells reducing the concentration of specific aminoacylable tRNA. Therefore, the extent of inhibition is associated with the rate of starvation for a specific tRNA. Here, we used minigenes harboring various last sense codons that sequester specific tRNAs with different efficiency, to inhibit the translation of reporter genes containing, or not, these codons. A prompt inhibition of the protein synthesis directed by genes containing the codons starved for their cognate tRNA (hungry codons) was observed. However, a non-specific in vitro inhibition of protein synthesis, irrespective of the codon composition of the gene, was also evident. The degree of inhibition correlated directly with the number of hungry codons in the gene. Furthermore, a tRNA(Arg4)-sequestering minigene promoted the production of an incomplete beta-galactosidase polypeptide interrupted, during bacterial polypeptide chain elongation at sites where AGA codons were inserted in the lacZ gene suggesting ribosome pausing at the hungry codons.
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PMID:Codon-specific and general inhibition of protein synthesis by the tRNA-sequestering minigenes. 1648 66