Bats have been recognized as the natural reservoirs of a large variety of viruses. Special attention has been paid to bat coronaviruses as the two emerging coronaviruses which have caused unexpected human disease outbreaks in the 21st century, Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) and Middle East Respiratory Syndrome Coronavirus (MERS-CoV), are suggested to be originated from bats. Various species of horseshoe bats in China have been found to harbor genetically diverse SARS-like coronaviruses. Some strains are highly similar to SARS-CoV even in the spike protein and are able to use the same receptor as SARS-CoV for cell entry. On the other hand, diverse coronaviruses phylogenetically related to MERS-CoV have been discovered worldwide in a wide range of bat species, some of which can be classified to the same coronavirus species as MERS-CoV. Coronaviruses genetically related to human coronavirus 229E and NL63 have been detected in bats as well. Moreover, intermediate hosts are believed to play an important role in the transmission and emergence of these coronaviruses from bats to humans. Understanding the bat origin of human coronaviruses is helpful for the prediction and prevention of another pandemic emergence in the future.

The 5= cap structures of eukaryotic mRNAs are important for RNA stability and protein translation. T he 5= ends of eukaryotic cellular mRNAs and most viral mRNAs possess a cap structure, which plays important roles in mRNA splicing, intracellular RNA transport, RNA stability, and translation initiation (1). Host and viral RNA molecules lacking the 5= cap structure are rapidly degraded in the cytoplasm (2). The cap-0 structure of mRNA is cotranscriptionally formed through sequential enzymatic reactions, including RNA triphosphatase (TPase), RNA guanylyltransferase (GTase), and RNA (guanine-N7)-methyltransferase (N7-MTase) (1). In higher eukaryotes and some viruses, cap-0 structure m7GpppN-RNA is further methylated at the ribose 2=-O position of the nascent mRNA by a ribose 2=-O-methyltransferase (2=-O-MTase) to form a cap-1 structure (m7GpppNm) and cap-2 structure (m7GpppNmNm). Both N7-MTase and 2=-O-MTase can catalyze the transfer of the methyl group from the methyl donor S-adenosyl-L-methionine (SAM or AdoMet) to RNA substrate and generate S-adenosyl-L-homocysteine (SAH or AdoHcy) as a by-product. The functions of viral RNA cap structure include the following: (i) the guanosine cap core structure protects the 5=-triphosphate from activating the host innate immune response (3, 4); (ii) the N7 methylation is essential for viral replication through the enhancement of viral RNA translation (5); and (iii) the 2=-O methylation functions to

We report the isolation and characterization of a novel bat coronavirus which is much closer to the severe acute respiratory syndrome coronavirus (SARS-CoV) in genomic sequence than others previously reported, particularly in its S gene. Cell entry and susceptibility studies indicated that this virus can use ACE2 as a receptor and infect animal and human cell lines. Our results provide further evidence of the bat origin of the SARS-CoV and highlight the likelihood of future bat coronavirus emergence in humans.T he 2002-2003 outbreak of severe acute respiratory syndrome coronavirus (SARS-CoV) was a significant public health threat at the beginning of the 21st century (1). Initial evidences showed that the masked palm civet (Paguma larvata) was the primary suspect in the animal origin of SARS-CoV (2, 3). Later studies suggested that Chinese horseshoe bats are natural reservoirs and that the masked palm civet most likely served as an intermediate amplification host for SARS-CoV (4, 5). From our longitudinal surveillance of bat SARS-like coronavirus (SL-CoV) in a single bat colony of the species Rhinolophus sinicus in Kunming, Yunnan Province, China, we found a high prevalence of diverse SL-CoVs (6). Whole-genome sequence comparison revealed that these SL-CoVs have 78% to 95% nucleotide sequence identities to SARS-CoV, with the major differences located in the spike protein (S) genes and the region of open reading frame 8 (ORF8). We recently isolated a bat SL-CoV strain (WIV1) and constructed an infectious clone of another strain (SHC014); significantly, these strains are closely related to SARS-CoV and capable of using the same cellular receptor (angiotensin-converting enzyme 2 [ACE2]) as SARS-CoV (6, 7). Despite the high similarity in genomic sequences and receptor usage of these two strains, there is still some difference between the N-terminal domains of the S proteins of SARS-CoV and other SL-CoVs, indicating that other unknown SL-CoVs are circulating in bats.Here we report the isolation of a new SL-CoV strain, named bat SL-CoV WIV16. SL-CoV WIV16 was isolated from a single fecal sample of Rhinolophus sinicus, which was collected in Kunming, Yunnan Province, in July 2013. The full genomic sequence of SLCoV WIV16 (GenBank accession number KT444582) was determined and contained 30,290 nucleotides (nt) and a poly(A) tail which is slightly larger than those of SARS-CoVs and other bat SL-CoVs (6, 8-13). The WIV16 genome has a 40.9% GϩC content and short untranslated regions (UTRs) of 264 and 339 nt at the 5= and 3= termini, respectively. Its gene organization is identical to that of WIV1 and slightly different from that of the civet SARS-CoV and other bat SL-CoVs due to an additional ORF (name ORFx) detected between the ORF6 and ORF7 genes of the WIV1 and WIV16 genomes (data not shown). The conserved transcriptional regulatory sequence was identified upstream of ORFx, indicating that this is likely to be a potential functional gene. The overall nucleotide sequence of WIV16 has 96% identity (higher than that of any p...