To determine whether U insertions were present in the antisense genome, a two step RT-PCR was performed to specifically amplify only genomic RNA. Again, total RNA was extracted from a passage 4 stock of rhMPV/ΔM2-2 and the region from nt4536 in F to nt5623 in SH was amplified. 1 kb RT-PCR products were inserted in pCR2.1 and 15 individual plasmids were sequenced. All 15 cloned RT-PCR products contained an insertion of 1 or 2 T nts (antisense) in either the F gene (non-coding region), the M2-1 gene or the SH gene ( Figure 3C ). One sequence had an A inserted at nt4964 in the M2-1 gene. However, no insertions of C or G were observed. The 15 cloned RT-PCR products also contained 18 transitions and 4 transversions. Thus, there is a high frequency of U insertions in the genomic RNA suggesting that insertions were propagated in the viral genome. Whether the insertion events occurred during synthesis of the genomic or antigenomic RNA cannot be determined from these data.