A single Rep protein initiates replication of multiple genome components of faba bean necrotic yellows virus, a single-stranded DNA virus of plants

Faba bean necrotic yellows virus (FBNYV) belongs to the nanoviruses, plant viruses whose genome consists of multiple circular single-stranded DNA comp onents. Eleven distinct DNAs, 5 of which encode different replication initi ator (Rep) proteins, have been identified in two FBNYV isolates. Origin-spe cific DNA cleavage and nucleotidyl transfer activities were shown for Rep1 and Rep2 proteins in vitro, and their essential tyrosine residues that cata lyze these reactions were identified by site-directed mutagenesis. In addit ion, we showed that Rep1 and Repa proteins hydrolyze ATP, and by changing t he key lysine residue in the proteins' nucleoside triphosphate binding site s, demonstrated that this ATPase activity is essential for multiplication o f virus DNA in vivo. Each of the five FBNYV Rep proteins initiated replicat ion of the DNA molecule by which it was encoded, but only Rep2 was able to initiate replication of all the six other genome components. Furthermore, o f the five rep components, only the Rep2-encoding DNA was always detected i n 55 FBNYV samples from eight countries. These data provide experimental ev idence for a master replication protein encoded by a multicomponent single- stranded DNA virus.