Nucleic Acids Research, 1978, Vol. 5, No. 8 2877-2876
© 1978
Articles |
The relationship of SV40 replicating chromosomes to two forms of the non-replicating SV40 chromosome
Laboratory of Biology of Viruses, National Institute of Allergy and Infectious Diseases, National Institutes of Health Bethesda, MD 20014, USA
Received April 20, 1978.
SV40 replicating chromosomes were extracted from infected cells using a detergent free extraction method. This procedure also extracts 2 forms of the non-replicating chromosome, one of which corresponds to the well characterized 50–55S 5V40 minichromosome. The other is a more compact structure which has a sedimentation coefficient of 80–85S. The replicating chromosomes sediment between the 2 conformations of the mature chromosome. Electron microscopy of the replicating chromosomes suggests an overall conformation that resembles the 50–55S form of the mature chromosome rather than that of the 80–85S structure. Nucleosomes are present on both sides of the replication forks. When the replicating chromosomes were incubated in an in Vitro DNA synthesis assay all regions of the 5V40 genome were synthesized and a significant fraction of the replicating chromosomes completed replication. The progeny chromosomes co-sedimented with the 50–55S chromosomes which were present prior to the incubation. The sedientation coefficients and relative amounts of the two forms of the mature chromosome were unaffected by the incubation.
*Present Address: Department of Biochemical Science, Princeton University, Princeton, New York 08540 USA