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Translation
Published in Paul Pumpens, Single-Stranded RNA Phages, 2020
The ribosome releasing or recycling factor (RRF) was found by the translation of the R17 amB2 RNA having an UAG codon at the seventh triplet of the coat gene (Ogawa and Kaji 1975a,b). The RRF was purified to homogeneity, demonstrated a molecular mass of 23,500, and inhibited amino acid incorporation into proteins programmed by a mutant R17 amB2 RNA (Ryoji et al. 1981b). In this system, the major polypeptide formed in the absence of this factor had a molecular mass very close to the authentic R17 coat protein, suggesting that ribosomes may read through the amber codon in the absence of the RRF. It was shown further that, in the absence of the RRF, the ribosome, which has released the N-terminal hexapeptide at the amber codon, stood on the mRNA and subsequently reinitiated translation “in phase” immediately after the amber codon without formylmethionine (Ryoji et al. 1981a). However, the readthrough translation of the R17 amB2 coat gene occurred to some extent also in the presence of the RRF, as well as other termination factors (Ryoji et al. 1985). It was confirmed by peptide fingerprinting and amino acid sequencing that this coat-like protein was produced as a result of reinitiation of translation from the eighth codon, but not by amino acid misinsertion to the amber mutation codon. The readthrough by amino acid misinsertion in this system became predominant only when the Mg2+ concentration was higher than 16 mM (Ryoji et al. 1985).
C. elegans aversive olfactory learning generates diverse intergenerational effects
Published in Journal of Neurogenetics, 2020
Ana Goncalves Pereira, Xicotencatl Gracida, Konstantinos Kagias, Yun Zhang
rrf-3 mutants are depleted in the 26 G RNA population, which affects endogenous gene expression during spermatogenesis, oogenesis and zygotic development (Gent et al., 2010; Han et al., 2009; Lee et al., 2006). Thus, our results suggest that these rrf-3-mediated gene expression programs can be modulated by parental experience in a way that affects the behavior of the progeny. Furthermore, one of the prg-2 transcripts encodes a homolog of a C. elegans Argonaute/Piwi-related protein PRG-1 that regulates piRNAs. Despite the high level of similarity between prg-1 and prg-2, the function of prg-2 is not well understood (Ashe et al., 2012; Batista et al., 2008; Cox et al., 1998; Das et al., 2008; Lee et al., 2012; Wang & Reinke, 2008). Our study reveals a role of prg-2 in regulating parental learning experience-induced modulation of olfactory preference. Thus, we show that both the endo-siRNA and piRNA pathways play a role in the modulation of olfactory preference in progeny after 4-h maternal exposure. Whether they affect the expression of the same genes is however an open question. Behaviorally, while both mutations abolish the increased preference for PA14 in F1s as a result of training their mothers for 4 h, their phenotypes are slightly different. This observation suggests that they may act in different ways to regulate parental experience-induced behavioral changes.
Mechanisms of antimicrobial resistance in Stenotrophomonas maltophilia: a review of current knowledge
Published in Expert Review of Anti-infective Therapy, 2020
Teresa Gil-Gil, José Luis Martínez, Paula Blanco
Experimental evolution studies in the presence of increasing concentrations of tigecycline have revealed that the first step toward the acquisition of resistance to this antibiotic consists in the selection of mutations in the SmeDEF regulator gene, smeT [86]. It is important to state that the selected amino acid substitutions in SmeT have been already found in antibiotic resistant S. maltophilia clinical isolates [54,55], which validates the reliability of these in vitro experimental approaches. Besides smeDEF overexpression, tigecycline resistance in S. maltophilia is also acquired by mutations in the antibiotic target-coding genes: the ribosome 30 S subunits rpsU, rpsJ, and rpsA. All the tigecycline-evolved populations also have mutations in the ribosome recycling factor frr. A third set of genes was found to be mutated after exposure to tigecycline. These genes are related to lipopolysaccharide (LPS) biosynthesis and membrane homeostasis. It has been hypothesized that changes in the outer membrane composition of S. maltophilia can prevent the uptake of tigecycline, which diffuses through the membrane, thus leading to the observed low susceptibility of the mutants to these antibiotic [86].
Search for the Source of the Retinal Relaxing Factor
Published in Current Eye Research, 2018
Laura Vanden Daele, Charlotte Boydens, Joke Devoldere, Katrien Remaut, Johan Van de Voorde
Since the original observation in 1998,1 showing that isolated retinal tissue exerts a strong vasorelaxing influence on the blood vessel tone, several research groups have confirmed the existence of the so-called retinal relaxing factor(s) (RRF(s)).2–4 Despite many efforts to characterize this RRF, the nature and potential role in physiology and pathophysiology remain largely unknown. In addition, although some previous efforts were made to characterize the cellular source of the RRF, it remains unsettled which cell type(s) release(s) the RRF. 1 Therefore, the present study aimed to elucidate the cellular source of the RRF. Previously, it was reported that the neurotoxin tetrodotoxin, an inhibitor of tetrodotoxin-sensitive (TTX-S) voltage-dependent sodium (NaV) channels,5 did not affect the vasorelaxing influence of the retinal tissue. From this, it was concluded that the RRF is more likely released by glial cells than by neuronal cells.1 However, besides neuronal and glial cells, one has to keep in mind that most retinas contain a third cell type namely vascular cells, except for avascular retinas such as avian retinas.6 As in all previous studies on the RRF retinas from cows, pigs, dogs, sheep, rats, or mice were used, all containing vascular cells,1,2,7,8 the RRF may still be released from a retinal vascular cell. Therefore, in the present study, the vasorelaxing effect of chicken retinas, not containing blood vessels, was examined to exclude vascular cells as the cellular source of the RRF.