ISOLATION OF A HUMAN ROTAVIRUS CONTAINING A BOVINE ROTAVIRUS VP4 GENETHAT SUPPRESSES REPLICATION OF OTHER ROTAVIRUSES IN COINFECTED CELLS

Bovine-human reassortant strains containing ten human rotavirus gene s egments and segment 4, encoding VP4, of a bovine rotavirus were isolat ed from the stool of an infected Bangladeshi infant during cell cultur e adaptation. Two plaque purified variants of this reassortant, one ma king very large (429-L4) and the other tiny (429-S4) plaques, were fur ther analyzed. The electropherotypes of these variants were identical except for slight mobility differences in segment 4. The predicted seq uence of amino acids (aa) 16-280 in VP4 proteins revealed four differe nces between variants even in this limited region, so no single differ ence could be linked to plaque size. The small plaque variant S4 was p henotypically unstable and mutated to a large plaque-former within a s ingle cell culture passage. The predicted sequence of aa 16-280 of a l arge plaque variant derived from S4 revealed six changes, only one of which was common to that of the L4 strain, thus suggesting that multip le amino acid changes in VP4 may affect plaque size. Although the larg e plaque variant L4 grew faster and was released from cells more rapid ly than S4, its replication and that of other rotaviruses tested (i.e. RRV, NCDV and Wa) was suppressed by S4 in coinfected cells. Using an RRV x S4 reassortant containing only RRV segment 4, it was established that suppression was linked to the S4 VP4 protein. This suppression c ould not be associated with inhibition of viral adsorption and, theref ore, appeared to occur following internalization. Thus, a new property of the rotavirus VP4 protein has been identified in a bovine-human ro tavirus reas-sortant.