PREFERENTIAL SELECTION OF VP7 GENE FROM A PARENT ROTAVIRUS STRAIN (SA11) IN SEQUENTIAL PASSAGES AFTER MIXED INFECTION WITH SA11 AND SA11-HUMAN ROTAVIRUS SINGLE-VP7 GENE-SUBSTITUTION REASSORTANTS

We studied the competitive growth among SA11-L2(G3) and its single-hum an VP7 gene-substitution reassortants SA11-L2/KU-R1(G1) and SA11-L2/DS 1-R1(G2), which have the genetic background of SA11-L2, during sequent ial passages after mixed infection. When the same infectious units (m. o.i. of 5 p.f.u./cell) of SA11-L2 and a reassortant SA11-L2/KU-R1 were inoculated onto and passaged in MA104 cells, 88% of the virus clones isolated from the culture fluid at the 3rd passage belonged to G3, and all the clones from the 10th passage had G3 specificity. Even when SA 11-L2/KU-R1 with titer 10 times higher than that of SA11-L2 was used i n the coinfection, the predominance of clones with G3-VP7 was observed . Although G2 clones slightly surpassed G1 clones in number in the mix ed culture of SA11-L2/KU-R1 and SA11L2/DS1-R1, G3 clones predominated in the virus progeny from a mixed culture infected with the same titer s of SA11-L2, SA11-L2/KU-R1, and SA11-L2/DS1-R1. However, no significa nt difference in viral growth was detected among SA11-L2 and the two r eassortants.