The Cauliflower Mosaic Virus Minichromosome

Abstract

Plant viruses which contain DNA genomes have recently gained popularity as potential vehicles for introducing foreign DNA into plants (reviewed by Howell, 1982; Hohn et al., 1982). The most intensively studied of these DNA viruses is cauliflower mosaic virus (CaMV) which contains a double-stranded DNA genome of about 8 kilobases. The infective DNA purified from virus particles is circular, but not covalently closed (i.e., generally two to three site-specific discontinuities occur in the genome; Hull and Howell, 1978; Volovitch et al., 1978). One of the discontinuities occurs in the α-strand of CaMV DNA and is generally considered as map position 0/1 on the circular genome. The complementary or β-strand of CaMV DNA usually contains two discontinuities at map positions 0.20 and 0.53. In one case, however, the CM4-184 isolate of CaMV contains a deletion of about 421 base pairs in and around map position 0.20 which eliminates one of the discontinuities in the α-strand. In the virus particle, the DNA is surrounded by a protein capsid shell (reviewed by Hohn et al., 1982), but additional proteins such as histones or other chromosomal proteins are not associated with the encapsidated DNA.