Analyses of the mRNA transcription processes of snowshoe hare bunyavirus S and M RNA species.

The time course of synthesis of snowshoe hare bunyavirus small (S)- and medium (M)-sized viral RNA (vRNA), viral cRNA (vcRNA), and mRNA species was analyzed by using single-stranded DNA probes representing the S- and M-coded gene products. In the presence of puromycin, an inhibitor of protein synthesis, the subgenomic S mRNA species were detected, but not full-length S vcRNA or S vRNA species. No M-related RNA species were identified in puromycin-treated cells. In the absence of puromycin, full-length M and S vRNA, S vcRNA, and subgenomic S mRNA species were observed, as well as apparently full-length M vcRNA species, presumably including the approximately similar-sized M mRNA species. The 5' ends of the S and M mRNA species have been shown to be heterogeneous and some 12 to 17 bases longer than the ends of their corresponding presumptive replicative vcRNA species, in agreement with an earlier report that they represent nonviral primer sequences (D. H. L. Bishop, M. E. Gay, and Y. Matsuoko, Nucleic Acids Res. 11:6409-6418, 1983). The 3' ends of the M and S mRNA species were found to be shorter by some 60 and 100 nucleotides, respectively, than those of their corresponding full-length vcRNA species. Comparison of the 3' noncoding regions of the S and M vcRNA species revealed that there are conserved sequences following the translation termination codons of the two RNA species. One of these conserved sequences is a pyrimidine-rich template sequence that is approximately 20 nucleotides beyond the deduced S mRNA transcription termination site.