The S RNA genome segments of Batai, Cache Valley, Guaroa, Kairi, Lumbo, Main Drain and Northway bunyaviruses: sequence determination and analysis

Bunyaviruses have a genome comprising three segments of negative-sense RNA. The smallest RNA segment, S, encodes the nucleocapsid protein, N, and a nonstructural protein, NSs, in overlapping reading frames. The sequences of the S genome RNA segments of seven bunyaviruses (Batai, Cache Valley, Guaroa, Kairi, Main Drain, Northway and Lumbo) were determined from cloned cDNAs obtained using a one-step reverse transcription-PCR protocol. These sequences were compared to those of six viruses previously published, reinforcing earlier conclusions about relationships of the bunyaviruses. Sequence homologies between N proteins correlated with the subdivision of these viruses into three serogroups, Bunyamwera, California and Simbu. The encoded N proteins are either 233 or 235 amino acids in length, depending on the serogroup, whereas the NSs proteins are more variable (83 to 109 amino acids). Certain nucleotide sequence motifs are conserved in the S segments of the Bunyamwera and California serogroup viruses, including the spacing of the AUG initiation codons for the N and NSs proteins (except Guaroa virus), and a CA-rich motif in the virion-sense RNA just downstream of the predicted mRNA termination site. A duplicated sequence was observed in the 3' non-coding region of the Lumbo virus S segment, which accounts for the significantly longer S genome segment of this virus.