Definition: In this task, you're given a paragraph from the research paper and your task is to generate a suitable title for the research paper based on the given paper. Under 100 words is a good title length.
Input: The L protein of mononegaviruses harbours all catalytic activities for genome replication and transcription. It contains six conserved domains (CR-I to -VI; Fig. 1a ). CR-III has been linked to polymerase and polyadenylation activity, CR-V to mRNA capping and CR-VI to cap methylation. However, how these activities are choreographed is poorly understood. Here we present the 2.2-Å X-ray structure and activities of CR-VI þ , a portion of human Metapneumovirus L consisting of CR-VI and the poorly conserved region at its C terminus, the þ domain. The CR-VI domain has a methyltransferase fold, which besides the typical S-adenosylmethionine-binding site ( SAM P) also contains a novel pocket ( NS P) that can accommodate a nucleoside. CR-VI lacks an obvious cap-binding site, and the SAM P-adjoining site holding the nucleotides undergoing methylation ( SUB P) is unusually narrow because of the overhanging þ domain. CR-VI þ sequentially methylates caps at their 2 0 O and N7 positions, and also displays nucleotide triphosphatase activity.

ARTICLE X-ray structure and activities of an essential Mononegavirales L-protein domain