Expression and characterization of the 3a movement protein of cowpea chlorotic mottle bromovirus

Cowpea chlorotic mottle bromovirus (CCMV) 3a protein is required for cell-to-cell movement of the virus in host plants. The 3a protein was produced in Escherichia coli using an expression vector. Gel retardation analysis and UV cross-linking experiments demonstrated that the CCMV 3a protein (CC3a) bound single-stranded (ss) RNA cooperatively without sequence specificity. Binding competition analysis showed that CC3a bound ss-nucleic acids more strongly than double-stranded nucleic acids.