Banana bunchy top virus DNA-2 to 6 are monocistronic

Abstract

Banana bunchy top virus (BBTV) DNA-3 to 6 have each previously been shown to contain one large open reading frame in the virion sense, whereas no large ORF had been identified in BBTV DNA-2. RNAs transcribed from the BBTV genome were mapped using northern hybridisation and 3' RACE. One mRNA was transcribed from each of BBTV DNA-2 to 6 and four of these mRNAs mapped to the ORFs previously identified in BBTV DNA-3 to 6. The mRNA of BBTV DNA-2 was transcribed from a virion sense ORF probably using a TATA box sequence different to that in BBTV DNA-1, and DNA-3 to 6. This ORF encoded a 10 kDa protein of unknown function. The 3' untranslated region of the five mRNAs varied from 25 nucleotides (BBTV DNA-6) to 167 nucleotides (BBTV DNA-4) and each contained putative polyadenylation signals with associated GT rich sequence together with a possible termination signal (C/T/A)TGTAA conserved in all five mRNAs.

Reassortment and Concerted Evolution inBanana Bunchy Top VirusGenomes

“…However, the divergence of the CR-M within subgroups of DNA 1 and 3 is quite low (i.e., less than 3% variation within the two subclades of DNA 3 isolates but more than 11% divergence between the subclades) ( Table 2). It is worth noting that the ORF of DNA 2 proposed by Beetham et al (3) could not be detected from isolates reported from Hainan (ChiAY606084) or Taiwan (this study). In these isolates the proposed DNA 2 translation start codon is TTG instead of AUG. To avoid sequencing errors or mutation from a single clone of DNA 2, we sequenced other DNA 2 clones from the same isolate as well as from four individual isolates collected in Taiwan, but none contained a typical ATG start codon in the proposed position (data not shown).…”

Transcripts encoding the nanovirus master replication initiator proteins are terminally redundant

“…Another peculiar feature of these m-rep transcripts is that, among all predicted nanovirus mRNAs or mapped babuvirus transcripts (Beetham et al, 1997(Beetham et al, , 1999Herrera-Valencia et al, 2007), they have the longest 39-UTR sequences, which also comprise the IR sequences at the origin of replication. As ssDNA, the IR sequences potentially form a stem-loop structure.…”

“…Transcripts have only been mapped for BBTV (Beetham et al, 1997(Beetham et al, , 1999Herrera-Valencia et al, 2007). Transcript data for the legume-infecting nanoviruses are absent; only transcription initiation and termination signals on their respective DNAs have been recognized (Boevink et al, 1995;Katul et al, 1997;Sano et al, 1998; Shirasawa-Seo et al, 2005).…”

“…All Rep proteins recognize the origin of replication of viral DNA (ori) and cleave it in a conserved nonamer sequence, which is flanked by inverted repeats (IRs) (Timchenko et al, 1999). This way, the Rep proteins trigger the initiation of viral positive-strand DNA synthesis, which then continues by rolling-circle replication, very similar to their action in other ssDNA viruses (Laufs et al, 1995; Timchenko et al, 1999).Transcripts have only been mapped for BBTV (Beetham et al, 1997(Beetham et al, , 1999Herrera-Valencia et al, 2007). Transcript data for the legume-infecting nanoviruses are absent; only transcription initiation and termination signals on their respective DNAs have been recognized (Boevink et al, 1995;Katul et al, 1997;Sano et al, 1998; Shirasawa-Seo et al, 2005).…”

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).…”