the negative sense rna genome is in three segments. the l segment encodes the l endonuclease (an rna-dependent rna polymerase enzyme) for genome replication and mrna synthesis. the m segment encodes a polyprotein, further cleaved in the gn and gc surface glycoproteins for attachment and the nsm nonstructural protein that influences virulence. the s segment encodes the nss protein for immune suppression and virulence, and the n structural nucleocapsid protein.