Two mRNAs are transcribed from banana bunchy top virus DNA-1.

Abstract

We have mapped the mRNA transcripts of banana bunchy top virus (BBTV) DNA-1. Northern hybridization and 3h RACE analysis identified two polyadenylated RNAs associated with BBTV DNA-1. Previously, one major ORF in the virion sense of DNA-1 had been identified, which encoded a putative replication protein (Rep). An mRNA was identified in BBTV infected bananas that was clearly transcribed from this Rep ORF. Further, a second transcript was identified which mapped to an ORF completely within the Rep ORF. This encoded a putative 5 kDa protein of unknown function. Both these transcripts were also identified in a tobacco plant that had been transformed with Agrobacterium tumefaciens harbouring a binary construct containing the Rep ORF from BBTV DNA-1. This Rep ORF

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

“…Nicking and joining activities have recently been demonstrated for the Rep protein encoded by BBTV-C1 . A second virion-sense ORF, completely within the Rep protein ORF and encoding a putative 5 kDa protein, was also identified (Beetham et al, 1997). Five to six genome components of each nanovirus encode other putative viral proteins, and are referred to here as non-Rep components.…”

Banana bunchy top disease (BBTD) symptom expression in banana and strategies for transgenic resistance: A review

“…DNA-C encodes the cell cycle link protein (Clink) that has plant retinoblastoma-like binding ability to switch the host plant cells to S phase to make them more permissive for viral replication (Aronson et al, 2000;Wanitchakorn et al, 2000). The roles of the DNA-U3 gene product and that encoded by the small internal ORF of DNA-R are unknown (Burns et al, 1995;Beetham et al, 1997). Multiple satellite DNAs known as deficient DNA-R components (Briddon and Stanley, 2006) encoding non-essential Reps, which are capable of autonomous replication.…”

Reconstitution of Authentic Nanovirus from Multiple Cloned DNAs

“…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). An additional putative protein of unknown function appears to be encoded by a small internal open reading frame (ORF) embedded within the m-rep gene of BBTV, the sole exception to the "one DNA, one protein" rule for nano-and babuviruses (4). In addition to these bona fide integral genome components, additional Rep-encoding DNAs have been found associated with several nano-and babuvirus isolates (26,58).…”

“…Each circular ssDNA component is about 1 kb in size and is encapsidated in individual icosahedral particles. 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).…”