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The interaction between the rotavirus proteins viral protein 6 (VP6) and VP7 was examined in several exogenous protein expression systems. These proteins associated in the absence of other rotaviral proteins as demonstrated by a coimmunoprecipitation assay. Deletion analysis of VP7 indicated that truncations of either the mature amino or carboxyl terminus disrupted the proper folding of the protein and were not able to coimmunoprecipitate VP6. Truncation analysis of VP6 indicated that trimerization of VP6 was necessary, but not sufficient, for VP7 binding. MAb mapping and coimmunoprecipitation interference assays indicate that the VP6 amino acid residues between 271 and 342 are required for VP7 interaction. The interaction of VP6 and VP7 was also examined by the assembly of soluble VP7 onto baculovirus-expressed virus-like particles containing VP2 and VP6. Abrogation of this binding by preincubation of the particles with VP6 MAbs mapped to this same domain of VP6, validated our coimmunoprecipitation results. VP6 IgA MAbs that have been shown to be protective in vivo, but not a nonprotective IgA MAb, can interfere with VP7 binding to VP6. This suggests that these IgA MAbs may protect against rotavirus infection by blocking rotavirus assembly.