Identification of the cauliflower mosaic virus movement protein RNA-binding domain

The in vitro RNA-binding activity of the movement protein (P1) of cauliflower mosaic virus was studied after its expression in Escherichia coli, purification, and uv-crosslinking to a radioactive probe. It was found that insoluble P1 aggregates were involved in RNA-binding activity. A series of deletion mutants were used to identify a domain within P1 required for binding activity. The RNA-binding domain is located between amino acids 120 and 197 and includes the region of homology between P1 and the movement protein (P30) of tobacco mosaic virus (TMV). The homologous region corresponds to part of RNA-binding domain "A" in TMV P30, but unlike domain A, the P1 domain is able to bind RNA out of the context of the complete protein. The P1 RNA-binding domain shows some structural similarity with RNA-binding domains of other proteins. The conservation of this domain in the caulimo- and badnaviruses provides support for the view that this activity has biological relevance.