A novel human coronavirus: Middle East respiratory syndrome human coronavirus

Geng, HeYuan; Tan, WenJie

The novel coronavirus MERS-CoV is culturable and two complete genome sequences are now available. The complete genome sequence of the novel MERS-CoV contains 30119 nt and at least 10 predicted ORFs, which is similar to other HCoVs. The 5′-UTR and 3′-UTR contain 278 and 300 nt, respectively. Near the 5′ end, about 3/4 of the genome is occupied by two large ORFs, ORF1a (27913433 nt) and ORF1b (1343321514 nt). These two ORFs are translated from genomic mRNA to produce polyproteins pp1a and pp1ab by ribosomal frameshifting at the junction of ORF1a and ORF1b, with nt 13427 to 13433 predicted to form the "slippery sequence" (5′-UUUAAAC-3′) to produce polyproteins pp1ab. Downstream of ORF1b, the genome encodes four structure proteins, including the spike (S), envelope (E), membrane (M) and nucleocapsid (N) [17] . Four small non-structural ORFs (3a, 3b, 3c, 3d) lie between the S and E genes. The gene order of MERS-CoV is as follows: 5′-UTR-1a/1b-S-ORF3 (formed to 3a, 3b, 3c, 3d)-E-M-N-3′-UTR, which most closely resembles the gene structure of BatCoV-HKU4 and BatCoV-HKU5 (Figures 1 and 2 ).