Essential RNA binding and packaging domains of the Gag-Pol fusion protein of the L-A double-stranded RNA virus of Saccharomyces cerevisiae.

The crucial process in the assembly of the L-A double-stranded RNA virus is the recognition of its (+) single-stranded RNA by the Gag-Pol protein. The Pol region of this protein has RNA binding activity and is necessary for RNA packaging. Here we show that there are actually two in vitro RNA-binding domains of Pol (residues 172-190 and 770-819), and both are necessary for viral propagation, (but not for particle assembly). Furthermore, the N-terminal RNA-binding domain is necessary for in vivo packaging of viral (+) single-stranded RNA. We precisely define the extent of the Pol packaging domain (residues 67-213), which includes the N-terminal RNA-binding domain. This suggests that the N-terminal RNA-binding domain is responsible for binding the genomic RNA in the process of packaging and that additional surrounding residues are responsible for the specificity of binding.