Characterizing the interactions that SARS-CoV-2 viral RNAs make with host cell proteins during infection can improve our understanding of viral RNA functions and the host innate immune response. Using RNA antisense purification and mass spectrometry, we identified up to 104 human proteins that directly and specifically bind to SARS-CoV-2 RNAs in infected human cells. We integrated the SARS-CoV-2 RNA interactome with changes in proteome abundance induced by viral infection and linked interactome proteins to cellular pathways relevant to SARS-CoV-2 infections. We demonstrated by genetic perturbation that cellular nucleic acid-binding protein (CNBP) and La-related protein 1 (LARP1), two of the most strongly enriched viral RNA binders, restrict SARS-CoV-2 replication in infected cells and provide a global map of their direct RNA contact sites. Pharmacological inhibition of three other RNA interactome members, PPIA, ATP1A1, and the ARP2/3 complex, reduced viral replication in two human cell lines. The identification of host dependency factors and defence strategies as presented in this work will improve the design of targeted therapeutics against SARS-CoV-2.

Structural rearrangement of the activated spliceosome (B act ) to yield a catalytically active complex (B*) is mediated by the DEAH-box NTPase Prp2 in cooperation with the G-patch protein Spp2. However, how the energy of ATP hydrolysis by Prp2 is coupled to mechanical work and what role Spp2 plays in this process are unclear. Using a purified splicing system, we demonstrate that Spp2 is not required to recruit Prp2 to its bona fide binding site in the B act spliceosome. In the absence of Spp2, the B act spliceosome efficiently triggers Prp2's NTPase activity, but NTP hydrolysis is not coupled to ribonucleoprotein (RNP) rearrangements leading to catalytic activation of the spliceosome. Transformation of the B act to the B* spliceosome occurs only when Spp2 is present and is accompanied by dissociation of Prp2 and a reduction in its NTPase activity. In the absence of spliceosomes, Spp2 enhances Prp2's RNA-dependent ATPase activity without affecting its RNA affinity. Our data suggest that Spp2 plays a major role in coupling Prp2's ATPase activity to remodeling of the spliceosome into a catalytically active machine.[Keywords: spliceosome activation; DEAH-box helicase; Prp2; G-patch protein; Spp2; ATP hydrolysis] Supplemental material is available for this article. Pre-mRNA splicing proceeds by way of two phosphoester transfer reactions and is catalyzed by the spliceosome, which consists of the U1, U2, U4/U6, and U5 small nuclear ribonucleoproteins (snRNPs) and numerous nonsnRNP proteins (Wahl et al. 2009). Spliceosome assembly occurs de novo on each pre-mRNA and follows an intricate pathway involving major structural rearrangements during each round of splicing. The various remodeling steps are driven in yeast by eight conserved DExD/H-box ATPases/ RNA helicases. An interesting feature of the spliceosome is that it initially assembles into a multimegadalton ensemble-termed complex B-that contains all of the snRNPs but does not yet have an active site. Activation of the spliceosome is then initiated by the combined action of the Prp28 and Brr2 RNA helicases, yielding the B act complex. In this process, U1 and U4 snRNPs are displaced from the spliceosome, and new base-pair interactions between the U6 and U2 snRNAs and between U6 and the 59 splice site (59SS) are formed. The resulting RNA structure plays a central role in catalyzing both steps of pre-mRNA splicing (Staley and Guthrie 1998;Fica et al. 2013). During activation, 20 new proteins, including those of the NTC (nineteen complex), are stably integrated into the B act complex and stabilize the newly formed RNA-RNA interaction network (Chan et al. 2003;Chan and Cheng 2005;Fabrizio et al. 2009). The final catalytic activation of the spliceosome requires an additional ATP-dependent remodeling step, yielding complex B*. This step is catalyzed by the DEAH-box ATPase Prp2 (Kim and Lin 1996).Prp2 is structurally related to three other spliceosomal DEAH-box ATPases: Prp16, Prp22, and Prp43, which are involved, respectively, in the second catalytic step, the

1 1 a r t i c l e sSplicing entails the removal of introns from pre-mRNAs to generate exon-only mRNA, which is exported out of the nucleus for translation 1 . The splicing process is driven and controlled by a large and dynamic RNA-protein complex, the spliceosome 1,2 . The composition and structure of the spliceosome undergoes multiple rearrangements during a splicing reaction, in which a set of distinct structural and compositional states, designated as E, A, B act , B* and C complexes, can be defined 1 . As part of this process, small nuclear ribonucleoprotein (snRNP) particles and non-snRNP splice factors are recruited and released 1,2 . Although the organization of snRNP components of the spliceosome has received considerable attention in recent years, very little is known about the assembly, structure and dynamics of non-snRNP multimeric complexes.The non-snRNP RES complex is present in humans and yeast 3,4 . Deletion of RES genes slows splicing and leads to pre-mRNA leakage into the cytoplasm 3-5 . Distinct introns exhibit RES-dependent splicing 5-9 , as do pre-mRNAs encoding proteins functioning in RNA-nucleotide metabolism 8,10 . Components of the RES complex are found in B and C complexes of the spliceosome, in which RES can interact with U2 snRNP 4,11,12 . In yeast, the RES complex is composed of three proteins, snRNP-associated protein 17 (Snu17p, also known as Ist3p), pre-mRNA-leakage protein 1 (Pml1p) and bud siteselection protein 13 (Bud13p) 3,4 . Snu17p and Bud13p have been implicated directly in splicing 3,5,13 , whereas Pml1p has been linked to the retention of unspliced pre-mRNA in the nucleus 3,5 . Caenorhabditis elegans Bud13p is involved in embryogenesis 14 .Sequence analysis has indicated that Snu17p is a 148-residue (17.1-kDa) noncanonical member of the RRM family of proteins with a long C-terminal part, which exhibits low sequence similarity to published RRM structures 4 . Snu17p binds with nanomolar affinity to the 266-residue (30.5-kDa), natively disordered protein Bud13p 15 . The interaction has been postulated to involve a C-terminal UHM-ligand motif (ULM) in Bud13p that interacts with a U2AF-homology motif (UHM) in the RRM domain of Snu17p 13,15,16 . The only other identified domain encompasses a stretch of lysine residues at the N terminus of Bud13p. Binding of the third component, the 204-residue (23.4-kDa) Pml1p, occurs through its 50 N-terminal disordered residues. The remainder of Pml1p folds as a forkhead-associated domain 13,15,17 , which could potentially bind phosphopeptides 17 . Biochemical evidence has suggested that Snu17p acts as the central binding platform, which interacts with disordered parts of Bud13p and Pml1p 13,15,16 . The precise molecular architecture of the RES complex, however, has been elusive, and its RNA binding capabilities have remained unexplored.Here we solved the three-dimensional structure of the core of the RES complex and demonstrated that its assembly is driven by cooperativity that increases the binding affinity of the components of the complex ...

Little is known about contacts in the spliceosome between proteins and intron nucleotides surrounding the pre-mRNA branch-site and their dynamics during splicing. We investigated protein-pre-mRNA interactions by UV-induced crosslinking of purified yeast Bact spliceosomes formed on site-specifically labeled pre-mRNA, and analyzed their changes after conversion to catalytically-activated B* and step 1 C complexes, using a purified splicing system. Contacts between nucleotides upstream and downstream of the branch-site and the U2 SF3a/b proteins Prp9, Prp11, Hsh49, Cus1 and Hsh155 were detected, demonstrating that these interactions are evolutionarily conserved. The RES proteins Pml1 and Bud13 were shown to contact the intron downstream of the branch-site. A comparison of the Bact crosslinking pattern versus that of B* and C complexes revealed that U2 and RES protein interactions with the intron are dynamic. Upon step 1 catalysis, Cwc25 contacts with the branch-site region, and enhanced crosslinks of Prp8 and Prp45 with nucleotides surrounding the branch-site were observed. Cwc25’s step 1 promoting activity was not dependent on its interaction with pre-mRNA, indicating it acts via protein-protein interactions. These studies provide important insights into the spliceosome's protein-pre-mRNA network and reveal novel RNP remodeling events during the catalytic activation of the spliceosome and step 1 of splicing.

The Gram-negative rod-shaped bacterium Pseudomonas aeruginosa is not only a major cause of nosocomial infections but also serves as a model species of bacterial RNA biology. While its transcriptome architecture and posttranscriptional regulation through the RNA-binding proteins Hfq, RsmA, and RsmN have been studied in detail, global information about stable RNA-protein complexes in this human pathogen is currently lacking. Here, we implement gradient profiling by sequencing (Grad-seq) in exponentially growing P. aeruginosa cells to comprehensively predict RNA and protein complexes, based on glycerol gradient sedimentation profiles of >73% of all transcripts and ∼40% of all proteins. As to benchmarking, our global profiles readily reported complexes of stable RNAs of P. aeruginosa, including 6S RNA with RNA polymerase and associated product RNAs (pRNAs). We observe specific clusters of noncoding RNAs, which correlate with Hfq and RsmA/N, and provide a first hint that P. aeruginosa expresses a ProQ-like FinO domain-containing RNA-binding protein. To understand how biological stress may perturb cellular RNA/protein complexes, we performed Grad-seq after infection by the bacteriophage ΦKZ. This model phage, which has a well-defined transcription profile during host takeover, displayed efficient translational utilization of phage mRNAs and tRNAs, as evident from their increased cosedimentation with ribosomal subunits. Additionally, Grad-seq experimentally determines previously overlooked phage-encoded noncoding RNAs. Taken together, the Pseudomonas protein and RNA complex data provided here will pave the way to a better understanding of RNA-protein interactions during viral predation of the bacterial cell. IMPORTANCE Stable complexes by cellular proteins and RNA molecules lie at the heart of gene regulation and physiology in any bacterium of interest. It is therefore crucial to globally determine these complexes in order to identify and characterize new molecular players and regulation mechanisms. Pseudomonads harbor some of the largest genomes known in bacteria, encoding ∼5,500 different proteins. Here, we provide a first glimpse on which proteins and cellular transcripts form stable complexes in the human pathogen Pseudomonas aeruginosa. We additionally performed this analysis with bacteria subjected to the important and frequently encountered biological stress of a bacteriophage infection. We identified several molecules with established roles in a variety of cellular pathways, which were affected by the phage and can now be explored for their role during phage infection. Most importantly, we observed strong colocalization of phage transcripts and host ribosomes, indicating the existence of specialized translation mechanisms during phage infection. All data are publicly available in an interactive and easy to use browser.