Biology subjects

Mattei, S.

Publications and source records attributed to Mattei, S..

3 recordsLinked to original sources

bioRxiv2022

The translating bacterial ribosome at 1.55 A resolution by open access cryo-EM

Our understanding of protein synthesis has been conceptualised around the structure and function of the bacterial ribosome1-4. This complex macromolecular machine is the target of important antimicrobial drugs5, an integral line of defence against infectious diseases. Here, we describe how open access to state-of-the-art cryogenic electron microscopy facilities combined with bespoke user support offered by the newly established EMBL Imaging Centre enabled structural determination of the translating ribosome from Escherichia coli at 1.55 [A] 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 enables 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 [A] 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.

molecular biology↗

bioRxiv2022

Mechanism of RNA Polymerase I selection by transcription factor UAF

Pre-ribosomal RNA is selectively transcribed by RNA Polymerase (Pol) I in eukaryotes. The yeast transcription factor Upstream Activating Factor (UAF) represses Pol II transcription and mediates Pol I preinitiation complex (PIC) formation during the early stages of transcription initiation at the 35S ribosomal RNA gene. To unravel the DNA recognition and Pol I selection mechanisms of UAF, we determined the structure of UAF bound to native promoter DNA and transcription factor TBP. We found that UAF recognizes DNA using a hexameric histone-like scaffold with markedly different interactions than the nucleosome and the histone-fold-rich TFIID. UAF strategically sequesters TBP from DNA and Pol II/III-specific factors, and positions it for Core Factor binding, supporting Pol I recruitment. Our findings therefore reveal the molecular basis of Pol I selection for ribosome biogenesis. As well, they reveal an unexpected potential within the histone fold as a motif for specific protein-DNA interactions inside the cell.

molecular biology↗

bioRxiv2020

Cone-shaped HIV-1 capsids are transported through intact nuclear pores

Human immunodeficiency virus (HIV-1) remains a major health threat. Viral capsid uncoating and nuclear import of the viral genome are critical for productive infection. The size of the HIV-1 capsid is generally believed to exceed the diameter of the nuclear pore complex (NPC), indicating that capsid uncoating has to occur prior to nuclear import. Here, we combined correlative light and electron microscopy with subtomogram averaging to capture the structural status of reverse transcription-competent HIV-1 complexes in infected T cells. We demonstrate that the diameter of the NPC in cellulo is sufficient for the import of apparently intact, coneshaped capsids. Subsequent to nuclear import, we detected disrupted and empty capsid fragments, indicating that uncoating of the replication complex occurs by breaking the capsid open, and not by disassembly into individual subunits. Our data directly visualize a key step in HIV-1 replication and enhance our mechanistic understanding of the viral life cycle.

microbiology↗