To construct rhMPV/ΔM2-2/GFP and rhMPV/ΔM2-2/ GFPpolyA, an Nhe I site was introduced into the SwaIΔM2-2 subclone at nt5316, using the primer 5'GCACTAATCAAGTGCAGTGAGCTAGCATTTAAATTAG and its complement (the stop codon of M2-1 is in bold and the Nhe I site is underlined). The NheI-digested GFPcontaining NheI-N/P-GFP-NheI or NheI-N/P-GFP-PolyA-NheI cassette was inserted at nt5316 to generate rhMPV/ ΔM2-2/GFP or rhMPV/ΔM2-2/GFPpolyA respectively ( Figure 1C ).