Purified preparations of Belmont virus were shown to be very similar morphologically and biochemically to those of Bunyamwera virus. Comparisons of the synthesis of virus-specifed proteins in Vero and BHK-21 cells confirm the close taxonomic relationship. Total protein synthesis was inhibited 95% by 23 h post-infection with Belmont virus; a similar reduction occurred earlier in Bunyamwera virus-infected cells. This inhibition was multiplicity dependent, and synthesis of the host protein component was inhibited more severely. When cells were labelled late during infection at an m.o.i. of 1, the four structural proteins were readily resolved by gel electrophoresis. A small possibly non-structural protein (p14 for Belmont, p13 for Bunyamwera) was also identified late in infection in both hosts. As in the virion, the small envelope protein (P28) of Belmont virus was not glycosylated, whereas the large envelope protein G107, and the corresponding G1 and G2 of Bunyamwera virus, were labelled intracellularly in mannose, galactose and glucosamine. The kinetics of synthesis of the proteins for both viruses were similar, the events occurring earlier in Bunyamwera virus-infected cells. The nucleoprotein N was the most prominent at 3 to 5 h post-infection and remained so; G1 or the large envelope protein was also prominent early, but later more label was apparently incorporated into G2 or the small envelope protein. Pulse-chase experiments provided no evidence of precursor proteins. The relationship of the four or five identified virus-specified translation products to the three bunyavirus messenger RNAs remains obscure.


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