Programmed ribosomal frameshifting is a key event during translation of the SARS-CoV-2 RNA genome allowing synthesis of the viral RNA-dependent RNA polymerase and downstream proteins. Here we present the cryo-electron microscopy structure of a translating mammalian ribosome primed for frameshifting on the viral RNA. The viral RNA adopts a pseudoknot structure that lodges at the entry to the ribosomal mRNA channel to generate tension in the mRNA and promote frameshifting, whereas the nascent viral polyprotein forms distinct interactions with the ribosomal tunnel. Biochemical experiments validate the structural observations and reveal mechanistic and regulatory features that influence frameshifting efficiency. Finally, we compare compounds previously shown to reduce frameshifting with respect to their ability to inhibit SARS-CoV-2 replication, establishing coronavirus frameshifting as a target for antiviral intervention.
Our understanding of protein synthesis has been conceptualised around the structure and function of the bacterial ribosome. This complex macromolecular machine is the target of important antimicrobial drugs, an integral line of defence against infectious diseases. Here, we describe how open access to cryo-electron microscopy facilities combined with bespoke user support enabled structural determination of the translating ribosome from Escherichia coli at 1.55 Å resolution. The obtained structures allow for direct determination of the rRNA sequence to identify ribosome polymorphism sites in the E. coli strain used in this study and enable interpretation of the ribosomal active and peripheral sites at unprecedented resolution. This includes scarcely populated chimeric hybrid states of the ribosome engaged in several tRNA translocation steps resolved at ~2 Å resolution. The current map not only improves our understanding of protein synthesis but also allows for more precise structure-based drug design of antibiotics to tackle rising bacterial resistance.
Summary Very little is known about the aetiology of eccrine porocarcinoma (EP), a rare malignant sweat-gland tumour. Most reported cases have arisen de novo, or from a benign eccrine poroma. We report an unusual case, in which eccrine porocarcinoma arose at the exact site of pre-existing Bowen disease (BD).
Malignant mesothelioma of the tunica vaginalis is a rare but potentially fatal disease. Lack of characteristic clinical features and tumour markers makes the pre-operative diagnosis very difficult. A 54 year-old man with no history of exposure to asbestos presented with a short history of scrotal swelling and pain. Ultrasound revealed a suspicious nodularity involving his tunica vaginalis, suggestive of mesothelioma. Excisional biopsy revealed a malignant mesothelioma; hence the patient was treated with radical inguinal orchidectomy and hemiscrotectomy. We present a case of this rare tumour, its management and a review of the literature.
This case demonstrates the possibility of dual pathology in cases where metastatic disease is suspected. The use of small tissue samples may complicate diagnosis due to the heterogeneity of malignant tumours.
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