Viruses from 24 of the wells that exhibited fluorescence and that had been inoculated at a MOI of 0.1 were passaged once in Vero cells and each of the 24 viruses retained GFP expression. Total RNA was extracted from a mixture of cells plus supernatant and RT-PCR was performed to amplify a 1.5 kb fragment encompassing the GFPpoly A gene. The RT-PCR product was cloned into pCR2.1 and 8 individual clones were sequenced. 4 cloned GFP fragments contained the 11-nt CGA 6 TTA insert as constructed, 3 contained 1 inserted A that restored the reading frame of GFP, and 1 contained 3 inserted A nucleotides in the A 6 tract ( Figure 4F ). Thus, insertions of A nucleotides occurred frequently in non-hMPV sequences as well during rhMPV/ΔM2-2/GFPpolyA replication, suggesting that misincorporation of A nucleotides is not hMPV sequence-specific.