The nucleotide sequence of cloned wheat dwarf virus DNA

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Restriction analysis and cloning of virus-specific double-stranded DNA isolated from plants infected with wheat dwarf virus (WDV) indicated that the virus genome, like that of maize streak virus (MSV), consists of a single DNA circle. The complete nucleotide sequence of cloned WDV DNA (2749 nucleotides) has been determined. Comparison of the potential coding regions in WDV DNA with those in the DNA of two strains of MSV suggests that these viruses encode at least two functional proteins, the coat protein read in the virion (+) DNA sense and a composite protein, formed from two open reading regions, in the complementary (−) DNA sense. Although WDV and MSV are serologically unrelated their coat proteins showed 35% direct amino acid sequence and their DNAs showed 46% nucleotide sequence homology. There was too little homology between the DNAs of WDV and those of two geminiviruses with bipartite genomes, cassava latent virus (CLV) and tomato golden mosaic virus (TGMV), to align the sequences. However comparison of the amino acid sequences of predicted proteins of WDV, MSV, TGMV and CLV revealed clear relationships between these viruses and suggested that the monopartite and the bipartite geminiviruses have a common ancestral origin. Four inverted repeat sequences which have the potential to form hairpin structures of △G≥-14 kcal/mol were detected in WDV DNA. The sequence TAATATTAC present in the loop of one of these hairpins is conserved in similar putative structures in MSV DNA and in both DNA components of CLV and TGMV and may function as a recognition sequence for a protein involved in virus DNA replication.

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