mRNA Decapitation Induced by the Herpes Simplex Virus Virion Host Shutoff Protein

Abstract

Cells infected with herpes simplex virus show a rapid cessation of protein synthesis and a dramatic decline in the levels of mRNA; a process known as host shutoff. This effect is attributed to a viral tegument protein called the virion host shutoff protein, or vhs. The mechanism by which vhs induces mRNA degradation is not yet understood. It is not known whether vhs possesses RNase activities or if it acts in combination with other cellular factors. To gain a better understanding of the function of vhs, I examined RNA degradation in detail by analyzing the RNA decay products generated in the presence of vhs. 𝘐𝘯 𝘷𝘪𝘷𝘰 experiments, performed by infecting murine erythroid leukemia cells with HSV, revealed that beta-globin mRNA is rapidly degraded, in the presence of vhs, without being converted to detectable decay intermediates. The half-life of this mRNA was 15 and 60 minutes for HSV-2 and HSV-1, respectively. Using vhs translated in a rabbit reticulocyte lysate system, I found that vhs induced rapid decay at the 5' end of a capped RNA molecule. The decay event was endonucleolytic and occurred at preferred sites downstream of the cap, generating capped oligonucleotides. Unlike influenza RNA polymerase, the cleavage event did not occur at a fixed distance from the cap since capped oligos of differing size were generated from different RNA substrates. My data indicate that vhs induced cleavage exhibits a strong, but not absolute preference for RNAs possessing an m⁷G cap, which may account for vhs' specificity for m RNAs 𝘪𝘯 𝘷𝘪𝘷𝘰.