Banana bunchy top virus DNA-3 encodes the viral coat protein

Banana bunchy top virus (BBTV) has a multicomponent genome consisting of at least six circular single-stranded DNAs each with a single large open reading frame (ORF) in the virion sense. A protein of approximately 20 kDa has been associated with purified virions and is assumed to be the viral coat protein. The N-terminus of this protein was sequenced and compared to the predicted amino acid sequence of the large ORF of BBTV DNA-1 to 6. This comparison indicated that the ORF of BBTV DNA-3, which potentially encodes a protein of 19.3 kDa, was the coat protein gene of BBTV. The ORF sequence of BBTV DNA-3 was cloned into a prokaryotic expression vector, pMAL-c2, and the resulting maltose binding-BBTV coat protein fusion product was purified and used for the production of polyclonal antiserum in a rabbit. The resultant antiserum was able to detect the presence of BBTV in infected leaf tissue confirming that the large virion sense ORF of BBTV DNA-3 encodes the viral coat protein.