Schematic diagram of the M-F region in the morbillivirus genome. The M-F region extends from the M gene stop codon to the Fsp cleavage site (A↓QIHW residues). The intergenic region is indicated by the position of the CTT triplet, and the locations of in-frame F start codons are marked by arrowheads. The end of the M protein and the beginning of F2 subunit of the mature F protein are black, and the putative Fsp is gray. Measles virus is the type species of the genus Morbillivirus and the Edmonston strain (MeV; GenBank accession no. AF266288) is shown. Canine distemper virus (CDV strain 5804P; GenBank accession no. AY386316), Rinderpest virus (RPV; GenBank accession no. NC_006296), Peste-des-petits-ruminants virus (PRPV; GenBank accession no. NC_006383), Dolphin morbillivirus (DMV; GenBank accession no. NC_005283), and Phocine distemper virus (PDV; GenBank accession no. D10371) are shown below. Genome components are drawn to scale.