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The speed and accuracy of protein synthesis are fundamental parameters for understanding the fitness of living cells, the quality control of translation, and the evolution of ribosomes. In this study, we analyse the speed and accuracy of the decoding step under conditions reproducing the high speed of translation in vivo. We show that error frequency is close to 10−3, consistent with the values measured in vivo. Selectivity is predominantly due to the differences in kcat values for cognate and near-cognate reactions, whereas the intrinsic affinity differences are not used for tRNA discrimination. Thus, the ribosome seems to be optimized towards high speed of translation at the cost of fidelity. Competition with near- and non-cognate ternary complexes reduces the rate of GTP hydrolysis in the cognate ternary complex, but does not appreciably affect the rate-limiting tRNA accommodation step. The GTP hydrolysis step is crucial for the optimization of both the speed and accuracy, which explains the necessity for the trade-off between the two fundamental parameters of translation. 相似文献
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Corinna Richter Ron L. Dy Rebecca E. McKenzie Bridget N.J. Watson Corinda Taylor James T. Chang Matthew B. McNeil Raymond H.J. Staals Peter C. Fineran 《Nucleic acids research》2014,42(13):8516-8526
Clustered regularly interspaced short palindromic repeats (CRISPR), in combination with CRISPR associated (cas) genes, constitute CRISPR-Cas bacterial adaptive immune systems. To generate immunity, these systems acquire short sequences of nucleic acids from foreign invaders and incorporate these into their CRISPR arrays as spacers. This adaptation process is the least characterized step in CRISPR-Cas immunity. Here, we used Pectobacterium atrosepticum to investigate adaptation in Type I-F CRISPR-Cas systems. Pre-existing spacers that matched plasmids stimulated hyperactive primed acquisition and resulted in the incorporation of up to nine new spacers across all three native CRISPR arrays. Endogenous expression of the cas genes was sufficient, yet required, for priming. The new spacers inhibited conjugation and transformation, and interference was enhanced with increasing numbers of new spacers. We analyzed ∼350 new spacers acquired in priming events and identified a 5′-protospacer-GG-3′ protospacer adjacent motif. In contrast to priming in Type I-E systems, new spacers matched either plasmid strand and a biased distribution, including clustering near the primed protospacer, suggested a bi-directional translocation model for the Cas1:Cas2–3 adaptation machinery. Taken together these results indicate priming adaptation occurs in different CRISPR-Cas systems, that it can be highly active in wild-type strains and that the underlying mechanisms vary. 相似文献
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Genomic organization of the transposable element Tdd-3 from Dictyostelium discoideum. 总被引:1,自引:0,他引:1
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The transposable element Tdd-3 from D. discoideum has been described originally in 1984 (Poole and Firtel, 1984). Additional copies of this element were discovered in the course of a recent study on tRNA gene organization in D. discoideum. Five out of 24 independently isolated tRNA genes proved to be associated with Tdd-3 elements. The surprising observation that all the elements always occurred within the 3'-flanking sequences of the Dictyostelium tRNA genes suggested the possibility of a general position specific integration of Tdd-3 elements upon transposition. Therefore we isolated additional Tdd-3 elements from various genomic D. discoideum libraries in order to test this hypothesis. Several new Tdd-3 elements were found associated with various tRNA genes. Additionally we identified Tdd-3 elements organized in tandem array or in association with RED (Repetitive Element of Dictyostelium), another repetitive element recently identified by our laboratory. In all cases a B-box equivalent of the eukaryotic gene-internal RNA polymerase III promoter was identified upstream of all Tdd-3 elements. 相似文献
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Elvira D'Alessandro Corinna De Matteis Vaccarella Maria Luisa Lo Re Francesco Cappa Angela D'Alfonso Stefania Discepoli Maria Rosa Della Penna Giuseppe Del Porto 《Human genetics》1988,80(2):203-204
Summary Pericentric inversion of chromosome 19 has been found in several members of three unrelated families from a restricted geographical region. In one of the families, an additional pericentric inversion of chromosome 9 was observed. Reproductive problems, multiple abortions in two families and a neonatal death in the third, were present. A review of previously described cases is included, and the genetic risk connected with this type of rearrangement is also discussed. 相似文献
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Abstract Pseudomonas sp. strain RW611 utilized the ammonium salt of 2-sulfobenzoate as sole source of carbon, sulfur, nitrogen, and energy. The xenobiotic sulfo substituent was dioxygenolytically eliminated as sulfite, which was then slowly oxidized to sulfate. 2,3-Dihydroxybenzoate, which resulted from desulfonation underwent meta -cleavage, mediated by 2,3-dihydroxybenzoate 3,4-dioxygenase activity. This enzyme was inhibited by 3-chlorocatechol and 2,3,4-trihydroxybenzoate. 相似文献
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G Schumann I Zündorf J Hofmann R Marschalek T Dingermann 《Molecular and cellular biology》1994,14(5):3074-3084
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J Hofmann G Schumann G Borschet R G?sseringer M Bach W M Bertling R Marschalek T Dingermann 《Journal of molecular biology》1991,222(3):537-552
A total of 68 different tRNA genes from the cellular slime mold Dictyostelium discoideum have been isolated and characterized. Although these tRNA genes show features common to typical nuclear tRNA genes from other organisms, several unique characteristics are apparent: (1) the 5'-proximal flanking region is very similar for most of the tRNA genes; (2) more than 80% of the tRNA genes contain an "ex-B motif" within their 3'-flanking region, which strongly resembles characteristics of the consensus sequence of a T-stem/T-loop region (B-box) of a tRNA gene; (3) probably more than 50% of the tRNA genes in certain D. discoideum strains are associated with a retrotransposon, termed DRE (Dictyostelium repetitive element), or with a transposon, termed Tdd-3 (Transposon Dictyostelium discoideum). DRE always occurs 50 (+/- 3) nucleotides upstream and Tdd-3 always occurs 100 (+/- 20) nucleotides downstream from the tRNA gene. D. discoideum tRNA genes are organized in multicopy gene families consisting of 5 to 20 individual genes. Members of a particular gene family are identical within the mature tRNA coding region while flanking sequences are idiosyncratic. 相似文献