The G1 and G2 glycoproteins of La Crosse virus, a member of the Bunyavirus genus of the Bunyaviridae, are encoded as a single open reading frame (ORF) in the viral middle-sized RNA segment. The primary product from this ORF is processed, either cotranslationally or shortly after translation, into the two glycoproteins and a nonstructural protein, NSm, of unknown function. We have expressed La Crosse glycoproteins using vaccinia vectors and studied their processing and localization. When expressed in the native G2-NSm-G1 configuration, both G1 and G2 targeted to the Golgi apparatus as shown by their colocalization with wheat germ agglutinin and acquired resistance to endoglycosidase H. When expressed independently, G2 was targeted to the Golgi apparatus but G1 was retained in the endoplasmic reticulum, indicating that a G1-G2 association is required for Golgi targeting of G1. In contrast to results with other members of the Bunyaviridae, we found that expression of G1 and G2 from separate vectors did not lead to the transport of the G1-G2 complex to the Golgi. However, disruption of the NSm region with a foreign sequence did not interfere with transport of the complex. When a portion of the β-galactosidase gene was inserted in frame into NSm, the glycoproteins derived from this construct were processed and targeted properly and were capable of mediating cell-to-cell fusion.
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