Decapping enzyme required for the removal of the 5'-end m7GpppN cap tethered to viral and host mRNAs to allow their decay in cells. May therefore accelerate viral and cellular mRNA turnover to eliminate competing host mRNAs and allow stage-specific synthesis of viral proteins. Acceleration of the turnover of cellular transcripts may even promote the shutoff of host protein synthesis. Does not cleave unmethylated RNAs or RNAs shorter than 24 nucleotides (By similarity). Expressed in the early phase of the viral replicative cycle. Belongs to the Nudix hydrolase family.