Amino acid substitutions in the effector domain of the γ 134.5 protein of herpes simplex virus 1 have differential effects on viral response to interferon-α

Abstract

The γ 134.5 protein of herpes simplex virus 1 (HSV-1) is a virus-encoded protein phosphatase 1 (PP1) regulatory protein that contributes to viral resistance to interferon. It functions to block the shutoff of protein synthesis mediated by the double-stranded RNA-dependent protein kinase. This requires the carboxyl terminus of the γ 134.5 protein to recruit PP1, forming a high-molecular-weight complex that dephosphorylates the α subunit of translation initiation factor eIF-2 (eIF-2α). In the present study, we introduced a series of point mutations into a region in the effector domain of the γ 134.5 protein, which is adjacent to the PP1-binding domain. Analysis of these mutants in virus-infected cells shows that Ser209Ala, Ser209Asp, Ser218Ala, or Trp219Tyr substitution does not affect viral response to interferon-α. In contrast, Arg215Leu or Ser218Asp substitution rendered the virus hypersensitive to interferon-α, which correlates with the inability of these γ 134.5 mutants to mediate dephosphorylation of eIF-2α. However, Arg215Leu or Ser218Asp substitution does not disrupt the formation of a high-molecular-weight complex required for eIF-2α dephosphorylation or binding of the γ 134.5 protein to PP1. These results suggest that concerted action of the PP1-binding domain and the effector domain of the γ 134.5 protein is required to confer HSV-1 interferon resistance.