Ten distinct circular ssDNA components, four of which encode putative replication-associated proteins, are associated with the faba bean necrotic yellows virus genome.

Four further circular ssDNA components (C7-C10), about 1 kb in size and structurally similar to the previously described components (C1-C6) found associated with a Syrian (Sy) isolate of faba bean necrotic yellows virus (FBNYV), have been identified. Similar to C1 and C2, two of the new components (C7 and C9) encode putative replication-associated (Rep) proteins of 33.2 and 32.7 kDa, respectively, the former of which is 90% identical to the C10 Rep protein of milk vetch dwarf virus (MDV). C8 encodes a putative protein (17.4 kDa) whose function is unknown, but which is highly conserved between FBNYV and the other nanoviruses MDV, subterranean clover stunt virus and banana bunchy top virus. The putative protein (19.7 kDa) encoded by C10 contains an LXCXE motif, which is also present in the homologues of its relatives, suggesting that they may all interact with plant retinoblastoma-like proteins. Sequence information for seven components of an Egyptian (Eg) FBNYV isolate indicated that six of them share > 96% identity with FBNYV-Sy. However, the C1 Rep protein of FBNYV-Eg was only 63.5% identical to that of FBNYV-Sy, but was 88.3 % identical to the MDV-C2 Rep protein. We conclude that the FBNYV genome consists of seven to ten components, six of which encode non-Rep proteins. All ten components of the FBNYV genome, except the Rep components C2 and C9, had closely related counterparts in the MDV genome. In spite of this similarity, FBNYV and MDV appear to be distinct virus species.