E. coli strain Rosetta [DE3] (Novagen) was used for the expression of N TAIL constructs. Since the MV N gene contains several rare codons that are used with a very low frequency in E. coli, coexpression of N TAIL constructs with the plasmid pLysS (Novagen) was carried out. This plasmid, which supplies six rare tRNAs, carries also the lysozyme gene, thus allowing a tight regulation of the expression of the recombinant gene, as well as a facilitated lysis. Cultures were grown overnight to saturation in LB medium containing 100 mg/mL ampicilin and 17 mg/mL chloramphenicol. An aliquot of the overnight culture was diluted 1/25 in LB medium and grown at 37 C. At OD 600 of 0.7, isopropyl b-D-thiogalactopyranoside (IPTG) was added to a final concentration of 0.2 mM, and the cells were grown at 37 C for 3 h. The induced cells were harvested, washed, and collected by centrifugation. The resulting pellets were frozen at À20 C.