The major component of the MARV polymerase complex, L, has an estimated molecular weight of 267 kD [67] . It is essential for transcription and replication and together with VP35 forms the RNA-dependent RNA polymerase complex (see above, 7.3. Viral Proteins, VP35). L contains the enzymatic functions of the polymerase. The binding site for VP35 has been mapped to the N-terminal 530 amino acid residues of L [115, 134] . The L proteins of the NNS RNA viruses are highly conserved multifunctional proteins, which are organized in functional domains [161] . Based on this conservation with other NNS RNA polymerases, MARV L is believed to carry out RNA synthesis, capping, and polyadenylation of viral mRNAs although these functions have not been shown experimentally.