Discussion
The phylogenetic analysis shows that camel and human MERS-CoVs are clustered together. The human-camel MERS-CoV cluster is further divided into two clades, i.e. clade A and clade B. The earliest cases of MERS including EMC/2012 and Jordan-N3/2012 belong to clade A clusters, and all other cases from 2012-2015 are in clade B (7, 8). Being distinct from phylogenetic analysis, which is biasedly based on the coding sequence, characterization of conserved pyrimidine nucleotide in the non-coding 5’-UTR of MERS-CoV may represent another possible mechanism in virus adaptive evolution since the conserved nucleotide sequence and structure of 5’-UTR directly interact with the host cellular factors during virus replication to regulate transcription, translation, and genomic RNA synthesis. A total of 10 complete genomes of MERS-CoV were reported in 2012 and classified into 2 clades (clade A and clade B) in phylogenetic analysis (7). However, all of them are the U—-U type virus according to the conserved pyrimidine nucleotide in 5’-UTR. Thus, the conserved pyrimidine nucleotides in 5’-UTR can serve as a novel genetic signature in evolution of MERS-CoV.
There are no specifically effective therapeutics and vaccines for MERS. In general, surveillance for MERS-CoV in humans and camels in affected countries is still a priority for infection control. In addition to the coding sequence, the variations in non-coding region, particularly in the conserved stem-loop region of 5’-UTR can offer novel implication in epidemiology. Its importance needs an attention without contempt in both tracing the chain of infection transmission and algorithm of phylogenetic analysis.