Characterization of La Crosse virus small-genome transcripts.

With restriction fragments from DNA clones of the La Crosse virus S genome segment, the 3' end of the S mRNA was located by S1 nuclease mapping near a polyuridine tract, approximately 100 nucleotides, from the end of the S genome. Genome replication in La Crosse virus-infected cells was abolished by the drug cycloheximide, similar to other negative-strand RNA viruses. However, the synthesis of S mRNA could not be detected in cells pretreated with cycloheximide, suggesting that ongoing protein synthesis is required for La Crosse virus genome transcription and replication. Primer extension experiments in the presence of chain-terminating nucleoside triphosphates demonstrated that the 5' end of the La Crosse virus S mRNA begins 10 to 14 nucleotides before the 3' end of the S genome segment, suggesting that the La Crosse virus S mRNA is initiated on a host primer. A hypothesis consistent with these unexpected findings is presented.