Infectivity of plasmids containing brome mosaic virus cDNA linked to the cauliflower mosaic virus 35S RNA promoter.

Full-length biologically active cDNAs of brome mosaic virus genomic RNAs 1, 2 and 3 were constructed by joining cDNA fragments. The cDNAs were constructed so that, at the 5' ends, unique SnaBI sites were present at the site of initiation of transcription. The cDNAs were inserted between a modified cauliflower mosaic virus (CaMV) 35S RNA promoter and terminator regions derived from CaMV DNA, and cloned into pUC18. When a mixture of the plasmid DNAs was inoculated onto Chenopodium hybridum leaves, local lesions appeared 5 to 6 days later. However, no symptoms appeared in similarly inoculated barley plants. Plasmid cDNAs with extra sequences at the 5' end were infectious but RNAs transcribed from cDNAs with similar sequences were not.