Isolation of a human rotavirus containing a bovine rotavirus VP4 gene that suppresses replication of other rotaviruses in coinfected cells.

Bovine-human reassortant strains containing ten human rotavirus gene segments and segment 4, encoding VP4, of a bovine rotavirus were isolated from the stool of an infected Bangladeshi infant during cell culture adaptation. Two plaque purified variants of this reassortant, one making very large (429-L4) and the other tiny (429-S4) plaques, were further analyzed. The electropherotypes of these variants were identical except for slight mobility differences in segment 4. The predicted sequence of amino acids (aa) 16-280 in VP4 proteins revealed four differences between variants even in this limited region, so no single difference could be linked to plaque size. The small plaque variant S4 was phenotypically unstable and mutated to a large plaque-former within a single cell culture passage. The predicted sequence of aa 16-280 of a large plaque variant derived from S4 revealed six changes, only one of which was common to that of the L4 strain, thus suggesting that multiple amino acid changes in VP4 may affect plaque size. Although the large plaque variant L4 grew faster and was released from cells more rapidly 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 could not be associated with inhibition of viral adsorption and, therefore, appeared to occur following internalization. Thus, a new property of the rotavirus VP4 protein has been identified in a bovine-human rotavirus reas-sortant.