IN-VITRO SELECTION OF PACKAGING SITES IN A DOUBLE-STRANDED-RNA VIRUS

The Saccharomyces cerevisiae double-stranded RNA virus ScVL1 recognize s a small sequence in the viral plus strand for both packaging and rep lication. Viral particles will bind to this viral binding sequence (VB S),vith high affinity in vitro. An in vitro selection procedure has be en used to optimize binding, and the sequences isolated have been anal yzed for packaging and replication in vivo. The selected sequence cons ists of a stem with a bulged A residue topped by a loop of several bas es. Four residues of the 18 bases are absolutely conserved for tight b inding. These all fall in regions that appear to be single stranded. E ight more residues have preferred identities, and six of these are in the stem, The VBS is similar to the R17 bacteriophage coat protein bin ding site, Packaging and replication require tight binding to viral pa rticles.