Figure 3

Deletions in NA RNA as viruses were passaged at limiting dilution or at moi of 0.01. RT-PCR products of NA genes from different passages amplified from viral cDNA were separated on a 1% agarose gel and stained with ethidium bromide. A and B: A/OK/323/03. A. Lane1, 1 kb ladder; lanes 2–6 are P₁-P₅; H = higher multiplicity (moi = 0.01) passages; L = limiting dilution passages. Limiting dilution passages retained the full length NA band, but passages at higher moi had little full length band and showed faster migrating bands resulting from internal deletions of the NA RNA segment. B. PCR products after further passages. 10H+1L is 10 passages at 0.01 moi followed by one passage at limiting dilution; 11L is limiting dilution passage 11; 10H+2L is 10 passages at high moi followed by two at limiting dilution; 12L is limiting dilution passage 12. C. A/OK/1992/05. Lanes are the same as panel A with the addition of negative (no RNA) and positive controls. Deletions are seen at P2 and higher but there is only minor decrease in full length NA at the higher multiplicity compared to limiting dilution.