Biology subjects

Adly, A.

Publications and source records attributed to Adly, A..

2 recordsLinked to original sources

bioRxiv2023

Assembly of SARS-CoV-2 ribonucleosomes by truncated N* variant of the nucleocapsid protein

The Nucleocapsid (N) protein of SARS-CoV-2 compacts the RNA genome into viral ribonucleoprotein (vRNP) complexes within virions. Assembly of vRNPs is inhibited by phosphorylation of the N protein SR region. Several SARS-CoV-2 variants of concern carry N protein mutations that reduce phosphorylation and enhance the efficiency of viral packaging. Variants of the dominant B.1.1 viral lineage also encode a truncated N protein, termed N* or {Delta}(1-209), that mediates genome packaging despite lacking the N-terminal RNA-binding domain and SR region. Here, we show that {Delta}(1-209) and viral RNA assemble into vRNPs that are remarkably similar in size and shape to those formed with full-length N protein. We show that assembly of {Delta}(1-209) vRNPs requires the leucine-rich helix (LH) of the central disordered region, and that the LH promotes N protein oligomerization. We also find that fusion of a phosphomimetic SR region to {Delta}(1-209) inhibits RNA binding and vRNP assembly. Our results provide new insights into the mechanisms by which RNA binding promotes N protein self-association and vRNP assembly, and how this process is modulated by SR phosphorylation.

microbiology↗

bioRxiv2022

Reconstitution of the SARS-CoV-2 ribonucleosome provides insights into genomic RNA packaging and regulation by phosphorylation

The nucleocapsid (N) protein of coronaviruses is responsible for compaction of the [~]30-kb RNA genome in the [~]100-nm virion. Cryo-electron tomography suggests that each virion contains 35-40 viral ribonucleoprotein (vRNP) complexes, or ribonucleosomes, arrayed along the genome. There is, however, little mechanistic understanding of the vRNP complex. Here, we show that N protein, when combined with viral RNA fragments in vitro, forms cylindrical 15-nm particles similar to the vRNP structures observed within coronavirus virions. These vRNPs form in the presence of stem-loop-containing RNA and depend on regions of N protein that promote protein-RNA and protein-protein interactions. Phosphorylation of N protein in its disordered serine/arginine (SR) region weakens these interactions and disrupts vRNP assembly. We propose that unmodified N binds stem-loop-rich regions in genomic RNA to form compact vRNP complexes within the nucleocapsid, while phosphorylated N maintains uncompacted viral RNA to promote the proteins transcriptional function.

biochemistry↗