Analysis of Six DNA Components of the Faba Bean Necrotic Yellows Virus Genome and Their Structural Affinity to Related Plant Virus Genomes

Abstract

Faba bean necrotic yellows virus (FBNYV) has a multicomponent circular ssDNA genome. In addition to a previously described genome component (C1) coding for a replicase-associated protein (Rep), five further components (C2 to C6) have now been identified. Each of the six components is about 1 kb in size, contains one major open reading frame (ORF) in the virion sense with a TATA box and polyadenylation signal, and has a noncoding region containing a highly conserved sequence possibly forming a stem-loop structure. Similar to C1, C2 encodes another putative Rep of 33.1 kDa, which is closely related to the Rep of banana bunchy top virus (BBTV). Based on bacterial expression and immunoblot analysis, the ORF of C5 encodes the capsid protein (CP) with a deduced molecular mass of 19 kDa. The FBNYV CP shares the highest amino acid (aa) identity (56.2%) with that of subterranean clover stunt virus (SCSV). The ORF of C4 potentially codes for a hydrophobic protein which appears to be structurally and functionally similar to the BBTV-C4 and SCSV-C1 proteins. No protein sequence similarities were found in databases for the C3 and C6 ORFs of FBNYV. FBNYV is clearly distinct from any known virus but is taxonomically related to BBTV and SCSV.

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

“…The FBNYV genome has been reported to consist of at least six circular ssDNA components, each of which is about 1 kb (Katul et al, 1995(Katul et al, , 1997 and is probably encapsidated in a separate particle.…”

Reconstitution of Authentic Nanovirus from Multiple Cloned DNAs

“…Experimental data and sequence evidence suggest that each DNA molecule, with a single exception, encodes only one protein (4,58). A set of five homologous genome components are common to both nano-and babuviruses: DNA-R encoding the master Rep (MRep) protein, which initiates rolling circle replication of all genomic DNAs of a nano-or babuvirus (25,53,55); DNA-S encoding the capsid protein (11,30,61); DNA-C encoding Clink, a cell-cycle link protein (3); DNA-M encoding a movement protein (60); and DNA-N encoding a nuclear-shuttle protein (60). Three other DNAs (DNAs-U1, -U2, and -U4) encoding proteins of as yet unknown functions have been identified from the nanoviruses FBNYV and MDV, and one further DNA (DNA-U3) was identified from the babuviruses BBTV (58) and ABTV (50).…”

Banana Bunchy Top Viral Coat Protein (CP) Gene Expression Studies at Molecular Level in Hill Banana cv. Sirumalai (AAB)

“…Molecular investigations on BBTV genome revealed that BBTV has isometric virions (Harding et al, 1991;Katul et al, 1997;Su et al, 2000), 18-20 nm in diameter, and a multicomponent genome consists of at least six circular single stranded DNA (ssDNA) component (BBTV DNA-1 to 6) ranging in size from 1108 bp to 1111 bp (Burns et al, 1994 andKaran et al, 1997;Wanitchakorn et al, 1997;Beetham et al, 1999). BBTV virions have a single coat protein of approximately 20 kDa (Thomas and Dietzen, 1991).…”