To construct rhMPV/GFPpolyA, an 11 nt Poly A insert was cloned into the NheI-N/P-GFP-NheI cassette using the primer 5' TGAGCTAGCTTAAAAAAGTGGGACAAGTCAAAATGGT-GCGAAAAAATTAAGCAAGGGCGAGG (hMPV P gene start sequences is in bold, the GFP sequences are italicized, and the 11 nt poly A insert is underlined) to generate the cassette NheI-N/P-GFP-PolyA-NheI. The NheI-N/P-GFP-PolyA-NheI cassette was ligated into the hMPV SphI/Cla I subclone at the Nhe I site located at nt5474. Again the StuI (nt4495) to ClaI (nt8693) fragment of the hMPV SphI/ Cla I subclone was inserted into the full-length cDNA to generate rhMPV/GFPpolyA ( Figure 1B) .