Institut des Sciences du Végétal, CNRS, 91198 Gif sur Yvette, France.
Tomato yellow leaf curl Sardinia virus (TYLCSV) is a begomovirus in the Geminiviridae family of single-stranded (ss)DNA viruses of plants. All ssDNA plant viruses characterized encode a class of related multifunctional replication initiator or Rep proteins that are essential for virus multiplication. These proteins catalyze the site-specific initiation of viral-strand DNA synthesis at the replication origin, bind specifically to double-stranded (ds)DNA, act as helicases, and interact with a variety of virus and host proteins. We used TYLCSV as representative begomovirus to study Rep protein functions. We mapped the origin-recognition, DNA-cleavage and nucleotidyl transfer activities of Rep to its amino-terminal 120 amino acids. By multidimensional heteronuclear magnetic resonance spectroscopy we determined the three-dimensional structure of this amino-terminal Rep domain. The structure revealed an unexpected similarity of the domain with the RNP/RRM domains of RNA-binding proteins, as well as with those of the (ds)DNA-binding domains of SV T-antigen or papilloma virus E1 protein.
To date, the three-dimensional structures of the DNA-binding domains of Rep proteins from the human parvovirus adeno-associated virus type 5, the porcine circovirus type 2 and the legume nanovirus faba bean necrotic yellows virus, determined by us and others, are available. They all share the same basic fold organisation with variations in some structural details. Hence, the DNA-binding domains of Rep proteins from ssDNA viruses infecting hosts as diverse as plants, pigs and primates characterize a family of proteins that may be considered as evolutionary intermediates between RNA-binding proteins and the more complex regulatory proteins of dsDNA viruses.
