Construction of cDNA for rhMPV/ΔM2-2, rhMPV/GFPpolyA and rhMPV/ΔM2-2/GFPpolyA. A) rhMPV/ΔM2-2 has a deletion in the M2-2 gene adjacent to a SwaI site. Nucleotides that were modified to introduce the SwaI site are underlined. Translational stop codons are bold and the intergenic (IG) sequence is bold italics. B) To construct rhMPV/GFPpolyA, an NheI site was introduced at the M2-2 stop codon of rhMPV and an NheI-N/P-GFP-polyA-NheI cassette was inserted. The modified nucleotides are underlined, the stop codon is bold and the IG sequence is bold italics. C) To construct rhMPV/ΔM2-2/GFPpolyA, an NheI site was introduced between the stop codon of M2-1 (bold) and the SwaI site (italics) in rhMPV/ΔM2-2 and an NheI-N/P-GFP-polyA-NheI cassette was inserted. The modified nucleotides are underlined and the IG sequence is in bold italics. D) The reading frame of GFP is aligned with that of GFPpolyA to show the stop codon and frame shift resulting from the 11 nt insertion.