Toscana virus genomic L segment: molecular cloning, coding strategy and amino acid sequence in comparison with other negative strand RNA viruses.

The complete nucleotide sequence of Toscana (TOS) virus (Bunyaviridae, Phlebovirus) L segment was determined. The L segment is 6404 nucleotides long, containing a single open reading frame (ORF) in the viral complementary sense coding for a protein of 2095 amino acids that, as in the case of negative strand RNA viruses, could be part of the RNA polymerase of TOS virus. This ORF is expressed by a messenger RNA (mRNA) as long as the genomic segment. Like the mRNAs expressed by the genomic segments of the other Bunyaviruses, the L mRNA has non-templated sequences at the 5' end. The comparison of TOS L protein sequence with the corresponding sequences of other negative strand RNA viruses showed a very high homology only with the Rift Valley Fever (RVF) virus. The residues conserved between the two proteins are mainly concentrated in the central region and contain three DD motifs proposed by Argos (1988) to be functional domains of DNA and RNA polymerases. The complete sequence of the Toscana virus L genomic segment has been deposited in the EMBL library with the accession number X68414.