A MAJOR REARRANGEMENT OF THE VP6 GENE OF A STRAIN OF ROTAVIRUS PROVIDES REPLICATION ADVANTAGE

During coinfection of BSC-1 cells with bovine rotavirus B223 and human rotavirus 69M and subsequent serial passages at low multiplicity of i nfection (0.1 m.o.i.), a reassortant virus (BMR) with a rearranged VP6 gene became the predominant strain. At passage 24 virus extracted fro m 50 of 51 plaques (98%) contained the rearranged gene 6, which had be en first observed in passage 19. The analyses of the clones obtained f rom passages before the appearance of the rearranged VP6 gene (passage 15) and after (passage 20) indicated that the B223 VP6 gene was the o rigin of the rearranged VP6 gene. To test whether the rearranged VP6 g ene was responsible for the selection advantage observed, reassortant C11 was generated with BMR and WA rotavirus, containing the rearranged VP6 gene and the other 10 genes from WA. Coinfection of WA rotavirus and reassortant C11 and subsequent serial passages at low m.o.i. resul ted in 100% of virus from clones extracted at passage 18 being identic al to reassortant C11; demonstrating that the rearranged VP6 gene was once again selected over the normal VP6 gene. The selection advantage of the rearranged VP6 gene could not be explained by comparison of the growth curves of the viruses, as there was no significant difference between the growth cycles of rotavirus B223 and reassortant BMR, nor b etween rotavirus Wa and reassortant C11. However, the plaque and elect ropherotype analysis at passage 1 of Wa and C11 coinfection revealed t hat 85% of the progeny viruses contained the rearranged gene 6. These data show that the gene 6 rearrangement resulted in selection of the r elevant reassortant, possibly by suppression of competitive strains, a nd may indicate a new mechanism for the evolution of rotavirus.