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RNA trisphosphatase and guanylyl transferase activities are associated with the RNA polymerase protein L of Rinderpest virus

Indian Institute of Science

¹ E-mail: shaila{at}mcbl.iisc.ernet.in

Rinderpest virus large protein (L) is an integral part of the ribonucleoprotein (RNP) complex of the virus responsible for transcription and replication of the genome. Previously, we have shown that recombinant L protein coexpressed along with P protein (as L-P complex) catalyses the synthesis of all viral mRNAs in vitro and the abundance of mRNAs follow a gradient of polarity, similar to what occurs in vivo. In the present work, we demonstrate that the viral mRNAs synthesized in vitro by the recombinant L or purified RNP are capped and methylated at the N7 guanine position. RNP from the purified virions as well as recombinant L protein shows RNA triphosphatase and Guanylyl transferase activities. L protein present in the RNP complex catalyses the removal of -Phosphate from in vitro generated triphosphate ended 25b RNA representing the viral N mRNA 5' sequence. The L protein forms a covalent enzyme-guanylate intermediate with GMP moiety of GTP whose formation is inhibited by the addition of pyrophosphate, thus exhibiting characteristics of cellular guanylyl transferases. The covalent bond between the enzyme and nucleotide is acid labile and alkali stable indicating the presence of phosphoamide linkage. The C-terminal region (aa 1717-2183) of RPV L alone exhibits the first step of guanylyl transferase activity of forming a covalent complex with GMP, though it lacks the ability to transfer GMP to substrate RNA. We describe biochemical characterization of the newly found RTPase/Guanylyl transferase activity of L protein.

Received 10 February 2009; accepted 16 March 2009.