INTRACELLULAR RNAS FOUND DURING BUNYAVIRUS INFECTIONS (RECOMBINANT, DNA, VIROLOGY).

Abstract

The family Bunyaviridae is the largest known taxonomic group of arboviruses. Four of the five genera possess members which are responsible for serious human and livestock disease. The worldwide distribution of these viruses justify studies which will allow understanding of the replication and transcription cycles within permissive cells. The bunyaviruses have been shown to possess a tripartite single strand RNA genome of negative polarity. Replication is confined to the cytoplasm and the virion envelope is acquired when the genome ribonucleoproteins bud into the golgi. Virus release is presumed to be through exocytosis and ultimately cell lysis. The messenger RNA species of all five genera do not possess a poly-A tail of sufficient length to bind to an oligo(dT) cellulose column. This has made separation of viral transcripts from replicating RNAs difficult. In an effort to achieve this separation, infected cell extracts were centrifuged over 20-40% CsCl gradients which permitted replicating RNA structures to band at a density of 1.32 while cellular and viral mRNAs pellet. Recovery of viral transcripts from the CsCl pelleted RNA required synthesis of a cDNA copy of the virus genome to use as a probe. This was done by an unusual method which employs both genome and antigenomic RNA as templates for reverse transcriptase in a first strand synthesis reaction. Recombinant viral clones were then used in a hybrid selection scheme to recover virus mRNA from pelleted material. After recovery, the messages were visualized on acid urea agarose gels pH 3.5, or used to program an in vitro translation reaction. Using these methods, it was established that each genome segment codes for a single messenger RNA which is most likely capped, and that for at least the mid sized segment, proteins with molecular weights which exceed the coding capacity of the genome are translated from the single message.