Sequences at four termini of the giardiavirus double-stranded RNA

The linear double-stranded RNA (dsRNA) genome of giardiavirus (GLV) was estimated to be 6100 nucleotides (nt) [Wang et al., Proc. Natl. Acad. Sci. USA 90 (1993) 8585-8599]. As the 5'- and 3'-untranslated regions (UTR) of viral genomes are known to contain critical information for viral replication, we reexamine the sequences at all four termini of GLV dsRNA by (i) direct RNA sequencing with RT, (ii) tailing GLV dsRNA with UTP or CTP in addition to ATP in 3' rapid amplification of cDNA ends (RACE) and (iii) adding poly(dG) to the products of primer extension in 5'-RACE. The results confirmed the reported sequence for the 5'-terminus of the GLV sense strand RNA, but uncovered an additional 177 nt at the 3'-terminus. The new study also showed conclusively that there are no protruding overhangs at either terminus of GLV dsRNA.