Evidence for a divided genome in bean golden mosaic virus, a geminivirus

Abstract

Gemini viruses1,2, a recently discovered group of plant viruses, are the only viruses containing circular single-stranded DNA (ssDNA) found in eukaryotic organisms. Their ssDNA, which is less than half the size (molecular weight (Mr) 7–8 × 105) (refs 3–6) of that of other ssDN A viruses7,8, is the smallest yet found in autonomously replicating viruses. Geminivirus DNA is encapsidated in paired isometric particles whose monomer units measure ∼18 nm. This unique capsid morphology was accounted for by an early hypothesis of a functionally divided genome. Among the RNA plant viruses, there are several groups that carry necessary genetic information on more than one nucleic acid species. In the case of geminiviruses, two nucleic acid components were postulated to be carried in each paired particle9,10. Analyses of the physical composition of geminiviruses showed, however, that there is only one DNA molecule in each paired particle6,11,12. We have now investigated the DNA of a geminivirus using restriction endonucleases and a biological assay of infectivity and report here evidence for a divided genome in bean golden mosaic virus (BGMV). Two different nucleotide sequences are found and both seem to be required for infectivity.