Differences in plaque size and VP4 sequence found in SA11 virus clones having simian authentic VP4.

We isolated five stable SA11 clones (TN-S1, TN-S2, TN-L1, TN-L2, and BN-S4) with different plaque sizes from two SA11 stocks. In polyacrylamide gel electrophoresis, the mobilities of the fourth, fifth, and seventh RNA segments of SA11 clones with large plaque size (TN-L1 and TN-L2) were faster than those of clones with small plaque size (TN-S1, TN-S2, and BN-S4). Nucleotide sequence determination of the fourth RNA segment identified a five-amino-acid difference in VP4s between the clones with large and small plaque sizes. The VP4 sequences of two clones with small plaque size (TN-S1 and BN-S4) were the same as the sequence of SA11-SEM reported by K. Nishikawa et al. (1988, J. Virol. 62, 4022-4026), while the VP4 sequences of the clones with large plaque size (TN-L1 and TN-L2) were similar, but not identical, to that reported by D. B. Mitchell and G. W. Both (1989, Nucleic Acids Res., 17, 2122). A single-gene reassortant, K8-L2.4, in which RNA segment 4 was derived from clone TN-L2 of SA11 virus and the other RNA segments were from strain K8, produced large plaques like TN-L2, suggesting that the five-amino-acid difference in VP4 between the clones with large and small plaque sizes might be associated with the difference in plaque size.