Intracellular forms of viral DNA consistent with a model of reverse transcriptional replication of the cauliflower mosaic virus genome.

Five unencapsidated, intracellular forms of cauliflower mosaic virus DNA which accumulate in infected turnip leaves are described. The forms are double stranded (or partially double stranded), and one (form iv) is a covalently-closed circular form of the full-length genome. Form i is an open form composed of full-length genome strands (7.6 kilobases) similar to encapsidated viral DNA. Form iii appears as a diffuse band on gels and is composed of two approximately half length strands (approximately 3.8 kb) spanning the region of the genome between the two site-specific DNA breaks (delta 1 and delta 2). Form ii is composed of a full length strand and an approximately half-length strand as described for form iii DNA. Form v is a small form (approximately 0.7 kilobase in undenatured form) that maps adjacent to the alpha-strand break (delta 1) and may be a foldback form. These forms appear to be intermediates in cauliflower mosaic virus DNA replication and the properties of these forms are consistent with possible intermediates in a model of reverse transcriptional replication of the viral genome.