Structural basis of mismatch recognition by a SARS-CoV-2 proofreading enzyme

Coronavirus 3′–5′ exoribonuclease (ExoN), residing in the nonstructural protein (nsp) 10-nsp14 complex, boosts replication fidelity by proofreading RNA synthesis and is critical for the virus life cycle. ExoN also recognizes and excises nucleotide analog inhibitors incorporated into the nascent RNA, undermining the effectiveness of nucleotide analog-based antivirals. Here, we present cryo-electron microscopy structures of both wild-type and mutant SARS-CoV-2 nsp10-nsp14 in complex with an RNA substrate bearing a 3′-end mismatch at resolutions ranging from 2.5 Å to 3.9 Å. The structures reveal the molecular determinants of ExoN substrate specificity and give insight into the molecular mechanisms of mismatch correction during coronavirus RNA synthesis. Our findings provide guidance for rational design of improved anti-coronavirus therapies.

Bilingual Advantage

A finding that has not received much attention in the metalinguistic awareness literature is that bilingual children may be better at identifying gender mismatches between a subject and a predicate. This phenomenon is not well understood, nor has it been studied systematically. In the present study we present a systematic investigation of the phenomenon involving all three levels of metalinguistic awareness (identification of the mismatch, correction and explanation) in a language pair that has not been tested previously. We tested a group of six-year-old Arabic–English bilingual children in comparison with two monolingual control groups. Results reveal that bilinguals performed better than monolinguals at the correction level. The study reveals a bilingual advantage in this population for the first time, while enhancing our knowledge of the development of metalinguistic awareness.

Problems of irradiance characteristics measurement of solar simulators for ground spacecraft tests

The reliability of both spacecraft as a whole and of their systems is confirmed at the stage of complex ground-based experimental tests, including complex thermal vacuum tests. The thermal state of the test object in thermal vacuum chambers is obtaining, in particular, using a solar simulator. Radiometers based on silicon photoelectric converters are most often used to control the irradiance of a solar simulator under conditions of thermal vacuum tests. At the same time, an analysis of the features of silicon photoelectric converters shows that their direct measurement with the accuracy required for ground-based tests of spacecraft is impossible; their output is nonlinear, depends on the received spectrum, their own temperature and has long-term instability. The achieved measurement accuracy directly depends on the number and accuracy of the tools used and the methods of the necessary correction, of which the mismatch correction between the solar simulator spectrum and the solar spectrum is the most difficult and laborious. At the same time, spectrally nonselective heat flux radiometers are free from the above disadvantages. In the course of the experiment we carried out, the significant dependence of the accuracy of measuring the irradiance with radiometers based on silicon photoelectric converters on the received spectrum was confirmed. The conclusion is made that direct measurement by heat flux radiometers of the irradiance of the solar simulator is most justified under the conditions of thermal vacuum tests.