Electron microscopic mapping of single-stranded discontinuities in cauliflower mosaic virus DNA by means of the biotin-avidin technique.

Biotin-labeled deoxyuridine triphosphate has been used to label the three natural single-stranded discontinuities of Cauliflower Mosaic Virus DNA. The presence of biotin permitted the direct visualization and mapping of the discontinuities by electron microscopy, using ferritin-labeled avidin.

A DNA polymerase activity is associated with Cauliflower Mosaic Virus.

A DNA polymerase activity is found within the Cauliflower Mosaic Virus (CaMV) particle. Analysis of the reaction product reveals that the linear form of the virion DNA is preferentially labelled. The molecular weight of the DNA polymerase as determined on an "activity gel" is 76 kDa.

Electron microscopic studies of the different topological forms of the cauliflower mosaic virus DNA: knotted encapsidated DNA and nuclear minichromosome.

Cauliflower mosaic virus (CaMV) DNA exists under different topological forms in infected plants. First, the population of encapsidated CaMV DNA molecules appears heterogeneous when analysed by gel electrophoresis. The electron microscopic study reported here reveals that CaMV virion DNA contains simple and multiple topological knots. Second, a supercoiled DNA form never found in virions exists as a chromatin-like nucleoprotein complex with nucleosome subunits in the nuclei of infected leaves. The compaction ratio of the minichromosomes is compatible with the nucleosomal structure, the number of nucleosomes (41.0 +/- 2.5) is in keeping with the length of the viral genome.

Free cauliflower mosaic virus supercoiled DNA in infected plants.

Evidence is presented indicating that free viral DNA exists in Cauliflower mosaic virus-infected leaves. Among the different viral DNA forms detected in total DNA extracts is a supercoiled form. We discuss its possible role in the replication process.