 It is present in SeV virions at relatively low levels (40 molecules/genome).The SeV genome is non-segmented, negative-sense RNA, of about 15.384 n. in length, and contains the noncoding 3’ leader and 5’ trailer regions, which are about 50 nucleotides in length.As in other respiroviruses from Paramyxoviridae family, in SeV they work as cis-acting elements essential for replication.