The putative transcription initiation site in giardiavirus double-stranded RNA genome

Little is known about mechanisms of RNA transcription from the RNA template of double-stranded (ds) RNA genome of Totiviridae family. The lack of knowledge can be attributed to technical difficulties in isolating infectious viral particles or transfecting host cells with viral genome or transcript. In the best studied case of L-A dsRNA virus of Saccharomyces cerevisiae (ScV), Fujimura and Wickner incubated the in vitro transcripts of viral cDNAs with empty viral, particles, and identified two cis sites in the (+)-strand viral RNA. A stem-loop in the 3'-terminal 30 nucleotide (nt) region is required for initiating replication of the (-)-strand RNA, whereas another stem-loop 400 nts upstream from the 3'-end binds to the gag-pol fusion protein. There was no transcription initiation site identified in the (-)-strand RNA.