mRNAs of Uukuniemi Virus, a Bunyavirus

Summary

Bunyaviruses are enveloped arthropod-borne viruses containing a tripartite single-stranded RNA genome of negative polarity. We have studied the strategy of gene expression of one member of this large family, namely Uukuniemi virus, the prototype of the genus Uukuvirus. Three mRNA species, which do not bind to oligo(dT)-cellulose, are found associated with polysomes of infected cells. Sucrose gradient and gel analyses, in vitro translation and molecular cloning have shown that: (i) The M virion RNA (vRNA) segment is transcribed into an mRNA of roughly the same size (Mr 1.1 × 10⁶) and encodes a precursor (p110) to the two glycoproteins G1 and G2. (ii) Sequence analysis of the 3′ end of the M vRNA, which is complementary to the 5′ end of the M mRNA, indicates an open reading frame starting from an AUG codon 18 nucleotides from the end of the mRNA. (iii) The S vRNA segment (Mr 0.5 × 10 ) is transcribed into a full-length plus-strand RNA (antigenome) and two small mRNA species (Mr about 0.3 × 10°) that encode a nonstructural (NS_S) protein (Mr 30,000) and the nucleocapsid (N) protein (Mr 25,000). Whether the two mRNA species contain overlapping nucleotide sequences is not known. By elimination, the L mRNA, transcribed from the L vRNA segment (Mr 2.4 × 10⁶), codes for the L protein (Mr 200,000) the putative RNA polymerase. The results obtained with Uukuniemi virus and other bunyaviruses indicate that the strategy of gene expression of these viruses in some aspects is different from that of other known RNA viruses.