Simian virus 40 (SV40) chromatin extracted from nuclei of infected monkey cells (CV1) was sedimented in neutral sucrose gradients, before and after digestion with bovine pancreatic RNase I-A or DNase I. DNA topoisomerase (TI) activity was found associated with RNase-resistant, DNase-sensitive SV40 nucleoprotein complexes. After polyacrylamide gel electrophoresis, a number of proteins with a molecular mass between 40 and 70 kDa were seen at the level of viral DNA peaks, some of which may represent catalytically active breakdown products of the TI enzyme. Large protein complexes were observed under the electron microscope in association with the viral chromosomes and appear to correspond to the SV40 DNA replication complex, including TI. Our results suggest that TI activity is indeed associated with the viral minichromosomes undergoing replication in vivo.
Murine adenovirus (MAd) type 1 strain FL and type 2 strain K87 genomes were cloned into plasmid pAT153 as HindIII restriction fragments. The MAd-1 and MAd-2 DNA genomes, 30"10kb and 34.71 kb in length respectively, were mapped using BgIII, ClaI, EcoRI, HindIII and SphI restriction endonuclease cleavage sites. In view of the large differences found between the MAd-1 and MAd-2 genomes in terms of the number and location of restriction sites, cross-hybridization experiments were performed. Homologous DNA sequences were located on the MAd-1 and MAd-2 physical maps. Both viruses are also genetically related to human adenovirus type 2 (HAd-2). Nucleotide sequences shared by HAd-2 and the MAds code for structural proteins, which may explain the antigenic similarities between these viruses from different origins. Our results confirm the existence of two distinct adenovirus species in the mouse.
The DNA of mouse adenovirus strain K87 (MAd-2) was cloned and mapped with restriction endonucleases BglII, ClaI, EcoRI, HindIII and SphI. Large differences were found between the MAd-2 and MAd-1 (strain FL) DNA molecules in terms of number and location of restriction sites. The MAd-2 genome also appeared as larger in size than the MAd-1 genome (34.72 kb vs. 30.14 kb). Our results confirm the existence of two distinct adenovirus species in the mouse. Hybridization experiments, on the other hand, indicate that both MAd-1 and MAd-2 are genetically related to human adenovirus type 2 (HAd-2). Overlapping regions of DNA homology are located in genes coding for HAd-2 structural components which could explain serological relationships observed between the human and the murine adenoviruses.
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