CHARACTERIZATION OF THE REOVIRUS LAMBDA-1 PROTEIN RNA 5'-TRIPHOSPHATASE ACTIVITY

Characterization of the phosphohydrolytic activities of recombinant re ovirus lambda 1 protein demonstrates that, in addition to the previous ly reported nucleoside triphosphate phosphohydrolase and helicase acti vities, the protein also possesses RNA 5'-triphosphatase activity, Thi s activity was absolutely dependent on the presence of a divalent cati on, Mg2+ or Mn2+, and specifically removes the 5'-gamma-phosphate at t he end of triphosphate-terminated RNAs, Kinetic competition analysis s howed that nucleoside triphosphate phosphohydrolase and RNA 5'-triphos phatase reactions are carried out at a common active site, These resul ts strongly support the idea that, in addition to its role as an RNA h elicase during transcription of the viral genome, lambda 1 also partic ipates during formation of the cap structure at the 5' end of newly sy nthesized reovirus mRNAs, The lambda 1 protein represents only the thi rd RNA triphosphatase whose primary structure is known and the first d escribed in a double stranded RNA virus.