Characterization of the Nucleoside Triphosphate Phosphohydrolase and Helicase Activities of the Reovirus λ1 Protein

Previous studies have shown that the reovirus lambda1 core protein harbors a putative nucleotide-binding motif and exhibits an affinity for nucleic acids. In addition, a nucleoside triphosphate phosphohydrolase activity present in reovirus cores has been recently assigned to lambda1 using gene reassortment analysis. In this study, it was demonstrated that the recombinant lambda1 protein, expressed in the yeast Pichia pastoris, is able to hydrolyze nucleoside 5'-triphosphates or deoxynucleoside 5'-triphosphates. This activity was absolutely dependent on the presence of a divalent cation, Mg2+ or Mn2+. The protein can also unwind double-stranded nucleic acid molecules in the presence of a nucleoside 5'-triphosphate or deoxynucleoside 5'-triphosphate. These results provide the first biochemical evidence that the reovirus lambda1 protein is a nucleoside triphosphate phosphohydrolase/helicase and strongly support the idea that lambda1 participates in transcription of the viral genome.