The virion host shutoff protein (U_L41) of herpes simplex virus 11 is an endoribonuclease with a substrate specificity similar to that of RNase A

Earlier, our laboratory reported that purified glutathione S-transferase-virion host shutoff (GST-vhs) protein exhibited endoribonucleolytic activity in in vitro assays using as substrates in vitro-transcribed regions of IEX-1 mRNA. Here, we report that studies of the cleavage patterns of synthetic RNA oligonucleotides defined the activity of GST-vhs as being similar to that of RNase A. Thus, GST-vhs cleaved the RNA at the 3′ end of single-stranded cytidine and uridine residues. Since the GST-mvhs nuclease-defective mutant protein failed to cleave the synthetic RNAs, the results unambiguously attribute the activity to vhs.