Two N-terminal regions of the Sendai virus L RNA polymerase protein participate in oligomerization

Abstract The RNA dependent RNA polymerase of Sendai virus consists of a complex of the large (L) and phosphoprotein (P) subunits where L is thought to be responsible for all the catalytic activities necessary for viral RNA synthesis. We previously showed that the L protein forms an oligomer [Smallwood, S., Cevik, B., Moyer, S.A., 2002. Intragenic complementation and oligomerization of the L subunit of the Sendai virus RNA polymerase. Virology 304, 235–245] and mapped the L oligomerization domain between amino acids 1 and 174 of the protein [Cevik, B., Smallwood, S., Moyer, S.A., 2003. The oligomerization domain resides at the very N-terminus of the Sendai virus L RNA polymerase protein. Virology 313, 525–536]. An internal deletion encompassing amino acids 20 to 178 of the L protein lost polymerase activity but still formed an L–L oligomer. The first 25 amino acids of paramyxovirus L proteins are highly conserved and site-directed mutagenesis within this region eliminated the biological activity of the L protein but did not have any effect on P–L or L–L interactions. Moreover deletion of amino acids 2–18 in L abolished biological activity, but again the L–L binding was normal demonstrating that the oligomerization domain of L protein resides in two N-terminal regions of the protein. Therefore, sequences between both aa 2–19 and aa 20–178 can independently mediate Sendai L oligomerization, however, both are required for the activity of the protein.