Correspondence

The genome of Bunyamwera virus (BUN; family Bunyaviridae, genus Orthobunyavirus) comprises three segments of negative-sense, single-stranded RNA. The RNA segments are encapsidated by the viral nucleocapsid (N) protein and form panhandle-like structures through interaction of complementary sequences at their 59 and 39 termini. Transcription and replication of a BUNgenome analogue (minireplicon), comprising the viral non-coding sequences flanking a reporter gene, requires just the viral RNA polymerase (L protein) and N protein. Here, sequences of Bunyamwera serogroupM segment RNAswere compared and conserved elements within nt 20–33 of the 39 and 59 non-coding regions that can affect packaging of minireplicons into virions were identified. RNA-folding models suggest that a conserved sequence within nt 20–33 of the 59 end of the genome segments maintains conserved structural features necessary for efficient transcription. Competitive packaging experiments using M, L and S segment-derived minireplicons that encode different reporter genes showed variable packaging efficiencies of the three segments. Packaging of a particular segment appeared to be independent of the presence of other segments and, for the S segment, packaging efficiency was unaffected by the inclusion of viral coding sequences in the minireplicon