Infectivities of native and cloned DNA of cauliflower mosaic virus

Infectivity assays on turnips reveal that (i) cauliflower mosaic virus (CaMV) DNA, whether circular or linear, is as infectious as the complete virus; (ii) linear DNA obtained with restriction enzymes from the native CaMV DNA has the same specific infectivity as when first cloned in plasmid (pBR322) or bacteriophage (lambda gtWES) vectors and then restricted at the cloning site; (iii) in all cases studied mosaic symptoms are accompanied by virus production. DNA isolated from these viruses is again circular and possesses the three "gaps" characteristic of CaMV DNA. The cloned CaMV DNA, when linked to the vector DNA, is noninfectious or exhibits very low infectivity.