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

A set of mutants affected in translational fidelity was constructed by transduction within an otherwise isogenic Escherichia coli B argF40 argR11 background. Alterations in ribosomal proteins S4, S5, S12 and L6 either as single mutations or in various combinations were compared for their effects on aminoglycoside phenotypes, on in vivo and in vitro misreading and on the rate of peptide bond formation. Results may be summarized as follows: (i) Strains carrying two ambiguity mutations on the ribosome without any restrictive mutation are viable. When together, they only weakly increase the level of mistranslation as judged by several in vivo and in vitro test systems. (ii) The combination of two ram mutations causes a very strong cooperative increase of streptomycin sensitivity, irrespective of whether the strains have a wild-type S12 or mutationally altered S12 proteins (of the drug-resistant or -dependent types) on their ribosomes; (iii) The S4 and S5 ram mutations do not alter the response of the ribosome to aminoglycosides of the 2-desoxystreptamine group which are structurally unrelated to streptomycin. This is interpreted in terms of an effect of these ram mutations on the streptomycin binding site but not on the site(s) of binding of the other aminoglycosides. (iv) The rate of polypeptide bond formation which was determined from the kinetics of beta-galactosidase induction is not significantly changed in strains bearing the ram and the strA (streptomycin-resistant) alleles. In contrast, the L6 and the strA (streptomycin-dependent) alleles strongly reduce the rate of polypeptide elongation which mechanistically might be connected with restriction of ambiguity (Nino, 1974) in these cases.
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PMID:Bacterial ribosomes with two ambiguity mutations: effects of translational fidelity, on the response to aminoglycosides and on the rate of protein synthesis. 10 18

Some of the spontaneous streptomycin-resistant mutants of Escherichia coli strain C600 exhibit pleiotropic effects in addition to the antibiotic resistance. These effects include decreased growth rates, reduced levels of certain enzymes, and poor support of bacteriophage growth. One of these mutants, strain SM3, was studied further. We have examined the question of whether the reduced growth rate of the mutant SM3 is related to the reduction in relative amounts of ribosomes or to the reduction in the efficiency of ribosomes in protein synthesis. Measurements of alpha, the differential synthesis rate of ribosomal protein, revealed that the protein synthesis effeciency of ribosomes from the mutant strain SM3 was reduced about twofold relative to that of the parent strain C600. Measurements of the induction lag for beta-galactosidase and of the synthesis time of several different molecular-weight classes of proteins indicated that the mutation resulted in a marked reduction in the peptide chain growth rate. This reduction in the chain growth rate probably accounted for most of the observed reduction in the growth rate of the mutant strain. These experimental results show that the strA gene product, the S12 protein of the 30S subunit, is involved in some aspect of protein chain elongation. Presumably this involvement occurs during the messenger ribonucleic acid-directed binding of transfer ribonucleic acid to the ribosome.
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PMID:Role of ribosomal protein S12 in peptide chain elongation: analysis of pleiotropic, streptomycin-resistant mutants of Escherichia coli. 32 23

Strains with a relA mutation together with three different alleles of spoT were used to study the effects of different levels of ppGpp on production time for beta-galactosidase, transcriptional polarity and readthrough of a stop codon by near-cognate tRNA or a suppressor tRNA. The influences of an rpsL(S12) allele and a miaA mutation, together giving decreased efficiency of translation, as well as an rpoB mutation, coding for an altered RNA polymerase, were also investigated. The spoT alleles which give total deficiency for ppGpp, or a level which is increased several-fold (Sarubbi et al. (1988) Mol. Gen. Genet. 213, 214-222), had at the most a marginal effect on the production time for a beta-galactosidase molecule or translational misreading of a nonsense mutation. The efficiency of an amber tRNA suppressor is not affected by ppGpp in strains with an otherwise wildtype translational machinery. These data suggest that ppGpp does not influence directly the translational process in vivo. Instead, ppGpp is found to interfere with transcriptional readthrough in a manner which is dependent on the rpsL224, miaA, as well as the rpoB mutations. Similarly, bacterial growth is affected by ppGpp in a manner which is dependent on properties of both the transcriptional and translational apparatus together. It is suggested that the primary effect of ppGpp is on transcriptional readthrough, but this effect is modified by translational/transcriptional coupling.
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PMID:Functional interactions between translation, transcription and ppGpp in growing Escherichia coli. 791 39

Archaea, Bacteria, and Eukarya have 34 homologous ribosomal protein (RP) families in common. Comparisons of published amino acid sequences prompted us to question whether RPs of the prokaryote Thermus thermophilus contain nuclear localization signals (NLSs), which are recognized by the nuclear import machinery of eukaryotic cells and are thereby translocated into the nucleoplasm ultimately accumulating in the nucleolus. Several RPs of T. thermophilus - specifically S12, S17, and L2 - were selected for this study since their three-dimensional structures as well as rRNA interaction patterns are precisely known at the molecular level. Fusion proteins of these RPs were constructed and subsequently expressed in COS cells. N-terminally tagged fusions with dimeric EGFP and C-terminally tagged hybrids with beta-galactosidase of prokaryotic RP S17 (S17p) were targeted to the nucleoplasm where they were visualized by direct fluorescence and by indirect immune staining, respectively. A region containing the classical monopartite NLS KRKR, which is known to physically interact with karyopherin alpha2, was delineated by tagging specific S17p fragments with beta-galactosidase. Unexpectedly, S12p and L2p hybrids accumulated in the nucleolus. Due to their size, RPs tagged with beta-galactosidase can only be imported into the nucleus when NLS-recognition is mediated by karyopherins since they are otherwise excluded from entry into the nucleoplasm of eukaryotic cells. Our results indicate that after the formation of the nuclear compartment during evolution, the newly established eukaryotic cell relied on the pre-existing basic amino acid clusters of the prokaryotic RPs for use as NLSs.
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PMID:Ribosomal proteins of Thermus thermophilus fused to beta-galactosidase are imported into the nucleus of eukaryotic cells. 1788 Oct 85

In ribosomal protein S12 mutant or L24 mutant the expression of lambdaN gene was depressed at translational level. To study its mechanism the lambdaN gene region of lambdaN -lacZ gene fusion was trimmed from its 5' end to 3' end with DNA exonuclease III (DNA exoIII) in order to alter the TIR (translational initiation region) and the coding region of lambdaN gene. After DNA sequencing 23 species of different lambdaN-lacZ fused genes were obtained. The beta-galactosidase activities of these deletants in ribosomal protein mutant were compared with that in wild type strain. The result indicated that (i) S12 mutant could affect 305 subunit's binding to the TIR of lambdaN gene messenger and cause the difficulty in forming 30s initiation complex and then decrease the efficiency of translational initiation; (ii) in S12 mutant the coding region of lambdaN gene also affected the expression lambdaN gene; (iii) in L24 mutant the inhibition of lambdaN gene expression was not related to translational initiation and the 5' end of the coding region of lambdaN gene, but related to the 3' end of lambdaN gene.
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PMID:Mechanism of regulating the expression of lambdaN gene by ribosomal protein at translational level. 1872 68