The genome sequence alignment of CoVs shows 58% identity on the nsp-coding region and 43% identity on the structural protein-coding region among different CoVs, with 54% at the whole genome level, suggesting the nsps are more conserved and the structural proteins are more divers in need of adaptation to new hosts. Since the mutation rates in the replication of RNA viruses are much higher than that of DNA viruses, the genomes of RNA viruses  are usually less than 10 kb in length. However, the CoV genome is much larger, with roughly 30 kb in length, the largest known RNA viruses.