An in-depth annotation of the newly discovered coronavirus (2019-nCoV) genome has revealed differences between 2019-nCoV and severe acute respiratory syndrome (SARS) or SARS-like coronaviruses. A systematic comparison identified 380 amino acid substitutions between these coronaviruses, which may have caused functional and pathogenic divergence of 2019-nCoV.

In a paper just published on Cell Host & Microbe by Aiping Wu et al, based on the first three determined genomes of the novel coronavirus (2019-nCoV), namely Wuhan/IVDC-HB-01/2019 (GISAID accession ID: EPI_ISL_402119) (HB01), Wuhan/IVDC-HB-04/2019 (EPI_ISL_402120) (HB04), and Wuhan/IVDC-HB-05/2019 (EPI_ISL_402121) (HB05), an in-depth genome annotation of this virus was performed with a comparison to related coronaviruses, including 1,008 human SARS-CoV, 338 bat SARS-like CoV, and 3,131 human MERS-CoV, whose genomes were published before January 12, 2020 (release date: September 12, 2019) from Virus Pathogen Database and Analysis Resource (ViPR) (http://www.viprbrc.org/) and NCBI.

Comparison of genomes of these three strains showed that they are almost identical, with only five nucleotide differences in the genome of ~29.8 kb nucleotides. The 2019-nCoV genome was annotated to possess 14 ORFs encoding 27 proteins. The orf1ab and orf1a genes located at the 5′-terminus of the genome respectively encode the pp1ab and pp1a proteins, respectively. They together comprise 15 nsps including nsp1 to nsp10 and nsp12 to nsp16. The 3′-terminus of the genome contains four structural proteins (S, E, M, and N) and eight accessory proteins (3a, 3b, p6, 7a, 7b, 8b, 9b, and orf14). At the amino acid level, the 2019-nCoV is quite similar to that of SARS-CoV, but there are some notable differences. For example, the 8a protein is present in SARS-CoV and absent in 2019-nCoV; the 8b protein is 84 amino acids in SARS-CoV, but longer in 2019-nCoV, with 121 amino acids; the 3b protein is 154 amino acids in SARS-CoV, but shorter in 2019-nCoV, with only 22 amino acids.

Further studies are needed to characterize how these differences affect the functionality and pathogenesis of 2019-nCoV.