In this task, you're given a paragraph from the research paper and your task is to generate a suitable title for the research paper based on the given paper. Under 100 words is a good title length.

[EX Q]: A new porcine coronavirus SADS-CoV was recently identified from suckling piglets 20 with severe diarrhea in southern China and its genome sequence is most identical (~95% 21 identity) to that of bat α-coronavirus HKU2. It again indicates bats are the natural 22 reservoir of many coronaviruses that have great potential for cross-species transmission 23 to animals and humans by recombination and/or mutation. Here we report the cryo-EM 24 structures of HKU2 and SADS-CoV spike glycoprotein trimers at 2.38 Å and 2.83 Å 25 resolution, respectively. HKU2 and SADS-CoV spikes exhibit very high structural 26 similarity, with subtle differences mainly distributed in the NTD and CTD of the S1 27 subunit responsible for cell attachment and receptor binding. We systematically 28 analyzed and compared the NTD, CTD, SD1 and SD2 domains of the S1 subunit and 29 the S2 subunit of HKU2 spike with those of α-, β-, γ-, and δ-coronavirus spikes. The 30 results show that the NTD and CTD of HKU2/SADS-CoV are probably the most 31 ancestral in the evolution of spike. Although the S2 subunit mediating membrane fusion 32 is highly conserved, the connecting region after fusion peptide in HKU2/SADS-CoV 33 S2 subunit also adopts a conformation distinct from other coronaviruses. These results 34 structurally demonstrate a close evolutionary relationship between HKU2 /SADS-CoV 35 and β-coronavirus spikes and provide new insights into the evolution and cross-species 36 transmission of coronaviruses. : bioRxiv preprint 39 Coronaviruses, categorized into the order Nidovirales family Coronaviridae and 40 subfamily Coronavirinae, are a large group of viral pathogens with a wide host range 1 . 41 Their infections in humans, other mammals and birds can cause respiratory, hepatic, 42 enteric and neurological diseases with varying severity 2 . The severe acute respiratory 43 syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus 44 (MERS-CoV) have posed severe threats to human health in the 21 st century 1,3 . In the 45 meantime, coronaviruses infecting domestic animals also bring substantial economic 46 losses 4 . For example, the swine acute diarrhea syndrome coronavirus (SADS-CoV) 47 (also known as SeACoV and PEAV) isolated in 2017 caused outbreaks of severe watery 48 diarrhea of suckling piglets with a mortality up to 90% in several commercial pig farms 49 in Guangdong Province of China 5-10 . SADS-CoV is an α-coronavirus and other 50 representative members in the α-genus are porcine epidemic diarrhea virus 51 (PEDV), porcine transmissible gastroenteritis coronavirus (TGEV), porcine respiratory 52 coronavirus (PRCV), human NL63 and 229E coronaviruses (HCoV-NL63 and HCoV-53 229E) 1 . Representative members in other three genera include mouse hepatitis 54 coronavirus (MHV), bovine coronavirus (BCoV), SARS-CoV, MERS-CoV, HCoV-55 OC43 and HCoV-HKU1 in the β-genus, avian infectious bronchitis virus (IBV) in the 56 γ-genus and porcine deltacoronavirus (PdCoV) in the δ-genus 1 . 57 Cross-species transmission promoted by genetic recombination and/or mutations 58 underlies the host range expansion of coronaviruses 3,11-13 . Bats are the natural reservoir 59 of more than 30 different α-and β-coronaviruses that have great potential for 60 interspecies transmission by recombination and/or mutation 12,14-16 . Data on genetic 61 evolution, receptor binding and pathogenesis have demonstrated that human SARS-62 CoV and MERS-CoV most likely originate from bats 1 . Palm civets and dromedary 63 camels are the intermediate hosts of SARS-CoV and MERS-CoV from bats to humans 1 , 64 respectively. The newly identified porcine SADS-CoV isolates are also found to share 65 ~95% sequence identity with Rhinolophus bat coronavirus HKU2, and this further 66 stressed the severe results of coronavirus spillover from bats to domestic animals 5-10 .
[EX A]: Cryo-EM structures of HKU2 and SADS-CoV spike 1 glycoproteins and insights into coronavirus evolution 2 3 4

[EX Q]: doi: bioRxiv preprint molecular biology. Our high-resolution data have enabled a precise study of transcription and translation in both pathogenic and attenuated forms of IBV, and expand our understanding of gammacoronaviral gene expression. We demonstrate that gene expression shows considerable intraspecies variation, with single nucleotide polymorphisms associated with altered production of sgmRNA transcripts, and our RiboSeq data sets enabled us to uncover novel ribosomally occupied ORFs in both strains. We also identify numerous cellular genes and gene networks that are differentially expressed during virus infection, giving insights into the host cell reponse to IBV infection. 3 47 48 49 50 51 52 53 54 55 56 author/funder. All rights reserved. No reuse allowed without permission.
[EX A]: Comparative analysis of gene expression in virulent and attenuated strains of infectious bronchitis virus at sub-codon resolution

[EX Q]: Background. The etiologic inference of identifying a pathogen in the upper respiratory tract (URT) of children with pneumonia is unclear. To determine if viral load could provide evidence of causality of pneumonia, we compared viral load in the URT of children with World Health Organization-defined severe and very severe pneumonia and age-matched community controls. Methods. In the 9 developing country sites, nasopharyngeal/oropharyngeal swabs from children with and without pneumonia were tested using quantitative real-time polymerase chain reaction for 17 viruses. The association of viral load with case status was evaluated using logistic regression. Receiver operating characteristic (ROC) curves were constructed to determine optimal discriminatory viral load cutoffs. Viral load density distributions were plotted. Results. The mean viral load was higher in cases than controls for 7 viruses. However, there was substantial overlap in viral load distribution of cases and controls for all viruses. ROC curves to determine the optimal viral load cutoff produced an area under the curve of <0.80 for all viruses, suggesting poor to fair discrimination between cases and controls. Fatal and very severe pneumonia cases did not have higher viral load than less severe cases for most viruses. Conclusions. Although we found higher viral loads among pneumonia cases than controls for some viruses, the utility in using viral load of URT specimens to define viral pneumonia was equivocal. Our analysis was limited by lack of a gold standard for viral pneumonia. Keywords. pneumonia; viral load; viral density; RSV; PERCH. For diagnosing viral pneumonia, upper respiratory tract (URT) specimens have become the most common specimen type due to their logistical ease of collection [1, 2]. However, detection of viruses in URT specimens has low specificity as this finding might simply reflect an URT infection without lower respiratory tract involvement or coincidental asymptomatic or past infection [2] [3] [4] . A possible solution to the lack of specificity of simply detecting the presence or absence of a virus in the URT of pneumonia patients is to determine whether the density of a virus in the URT can better distinguish its causative role in pneumonia. There are reports that a higher pathogen load in the URT is associated with pneumonia, for both Streptococcus pneumoniae S U P P L E M E N T A R T I C L E
[EX A]:
Clinical Infectious Diseases Clinical Infectious Diseases ® 2017;64(S3):S337-46 Is Higher Viral Load in the Upper Respiratory Tract Associated With Severe Pneumonia? Findings From the PERCH Study