Advances in RNA research and RNA nanotechnology depend on the ability to manipulate and probe RNA with high precision through chemical approaches, both in vitro and in mammalian cells. However, covalent RNA labeling methods with scope and versatility comparable to those of current protein labeling strategies are underdeveloped. A method is reported for the site- and sequence-specific covalent labeling of RNAs in mammalian cells by using tRNA(Ile2) -agmatidine synthetase (Tias) and click chemistry. The crystal structure of Tias in complex with an azide-bearing agmatine analogue was solved to unravel the structural basis for Tias/substrate recognition. The unique RNA sequence specificity and plastic Tias/substrate recognition enable the site-specific transfer of azide/alkyne groups to an RNA molecule of interest in vitro and in mammalian cells. Subsequent click chemistry reactions facilitate the versatile labeling, functionalization, and visualization of target RNA.

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BackgroundPyrazinamide (PZA) plays a unique role in the treatment for multidrug-resistant tuberculosis (MDR-TB) in both first- and second-line regimens. The aim of this study was to investigate the prevalence and molecular characterization of PZA resistance among MDR-TB isolates collected in Chongqing municipality.MethodsA total of 133 MDR-TB isolates were collected from the smear-positive tuberculosis patients who were registered at local TB dispensaries of Chongqing. PZA susceptibility testing was determined with a Bactec MGIT 960 system. In addition, the genes conferring for PZA resistance were screened by DNA sequencing.ResultsOf these 133 MDR-TB isolates, 83 (62.4%) were determined as PZA-resistant by MGIT 960. In addition, streptomycin- (83.1% vs. 56.0%, P < 0.01), ofloxacin- (51.8% vs. 18.0%, P < 0.01), kanamycin- (22.9% vs. 2.0%, P < 0.01), amikacin- (18.1% vs. 2.0%, P = 0.01), capromycin-resistance (12.0% vs. 2.0%, P = 0.05), were more frequently observed among PZA-resistant isolates compared with PZA-susceptible isolates. Sequence analysis revealed that 73 out of 83 (88.0%) MDR strains harbored a mutation located in the pncA gene, including 55 (75.3%, 55/73) of single nucleotide substitutions and 18 (24.7%, 18/73) of frameshift mutation, while no genetic mutation associated with PZA resistance was found in the rpsA gene. The pncA expression of strains harboring substitution from A to G at position −11 in the promoter region of pncA was significantly lower than that of H37Rv (P < 0.01).ConclusionsIn conclusion, our data have demonstrated that the analysis of the pncA gene rather than rpsA gene provides rapid and accurate information regarding PZA susceptibility for MDR-TB isolates in Chongqing. In addition, loss of pncA expression caused by promoter mutation confers PZA resistance in MDR-TB isolates.

Purpose and approach: We examine theoretically and experimentally how unequal abilities to contribute affect incentives and efficiency when players compete for membership in stratified groups based on the contributions they make. Players have either a low or a high endowment. Once assigned to a group based upon the contribution they have made, players share equally in their group's collective output. Depending upon the parameters, the mechanism has several distinct equilibria that differ in efficiency.Findings: Our theoretical analysis indicates that as long as certain assumptions are satisfied, efficiency should increase rather than decrease the more abilities to contribute differ. The analysis also suggests various follow-up experiments about equilibrium selection, tacit coordination, and the effect of unequal abilities in systems with endogenous grouping. We conduct an experiment that shows that subjects tacitly coordinate the mechanism's asymmetric payoff-dominant equilibrium with precision; this precision is robust to a change in the structure and complexity of the game.Implications: The results suggest that people respond to merit-based grouping in a natural way, and that competitive contribution-based grouping encourages social contributions even when abilities to contribute differ, which is the case in all communities and societies.

For a one-dimensional simple random walk (St), for each time t we say a site x is a favorite site if it has the maximal local time. In this paper, we show that with probability 1 three favorite sites occurs infinitely often. Our work is inspired by Tóth (2001), and disproves a conjecture of Erdös and Révész (1984) and of Tóth (2001).