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Previous studies have demonstrated that Hodgkin's, Burkitt's, and other human lymphomas contain particulate elements encapsulating 70S RNA and RNA-dependent DNA polymerase. [(3)H]DNA probes endogenously synthesized by these particles were used to demonstrate that the nuclear DNA of the lymphomas contain particle-related sequences that cannot be detected (less than 1/20th of a copy per genome) in the DNA of normal cells. This result agrees with our earlier findings in human leukemias. The data are inconsistent with any etiologic concept that invokes germ-line transmission of at least one complete copy of the particulate information associated with the malignancy. The unique sequences found in the nuclear DNA of Burkitt's and Hodgkin's tissues are related to each other but not to the DNA of the Epstein-Barr virus.

Digestion of mouse L cell mitochondrial DNA with EcoRI restriction endonuclease produces two linear duplex fragments comprising 86.3 +/- 2.0% and 14.2 +/- 1.0% of the circular genome length (16,000 +/- 470 nucleotide pairs). Digestion of human HeLa cell mitochondrial DNA with EcoRI produces three linear duplex fragments comprising 49.2 +/- 1.0%, 44.4 +/- 0.9%, and 6.4 +/- 0.4% of the circular genome length (16,590 +/- 710 nucleotide pairs). These fragments are shown to be generated by cleavage in unique regions of the mouse and human mitochondrial DNAs. An electron microscopic analysis of partially replicated molecules cleaved by EcoRI establishes a unidirectional mode of DNA replication for L cell mitochondrial DNA. The origin for DNA replication is located on the larger EcoRI fragment at a position that is 1,890 +/- 250 nucleotide pairs (11.8 +/- 1.2% of the circular genome length) from the proximal restriction site. Replication proceeds unidirectionally away from this restriction site throughout the length of the larger EcoRI fragment. Analysis of L cell, D-loop mitochondrial DNA cleaved by EcoRI indicates that a unique sequence is synthesized in formation of the D-loop in these nonreplicating molecules. The origin of D-loop synthesis is located on the larger EcoRI fragment at a position 1,760 +/- 180 nucleotide pairs (11.0 +/- 1.1% of the circular genome length) from the proximal restriction site and is, therefore, the origin for unidirectional displacement replication.

DNA synthesized by particulate fractions from human leukemic white blood cells has been subfractionated by hybridization to Rauscher leukemia virus 70S RNA followed by hydroxylapatite chromatography. The Rauscher-leukemia-virus-specific DNA fraction is shown to be complementary only to sequences present in the nuclear DNA of Balb/c mouse spleens infected by this virus and the nuclear DNA from human leukemic white blood cells, and not to sequences present in the nuclear DNA of normal Balb/c mouse spleens or the nuclear DNA of normal human white blood cells.

The topology of repeated sequences in mouse plasmocytoma DNA was studied by high-resolution CsCl density gradient centrifugation and heterogeneous nuclear RNA.DNA hybridization. Satellite region DNA of plasmocytoma cells contains additional components and hybridizes specifically with entire heterogeneous nuclear RNA molecules. A linkage is demonstrated between the A+T-rich satellite sequences and those hybridizing with heterogeneous nuclear RNA. Heavy DNA also hybridizes specifically with heterogeneous nuclear RNA molecules that show sequence similarity to heterogeneous nuclear RNA hybridized to satellite DNA. These results could suggest that part of satellite DNA became heavier after integration of some other DNA species, which could belong to a virus or to immunoglobulin repetitive genes. Dispersed, highly repetitive, short nucleotide sequences could constitute recognition sites for such a process.

Like HeLa DNA, L-cell DNA contains a significant number of unexpectedly long pyrimidine tracts. 1.3% of the thymidine residues of L-cell DNA are found in these long polypyrimidine tracts. Analysis of L-cell DNA fractions with different rates of reassociation indicates that polypyrimidine tracts are associated with "repeated" DNA. Longer pyrimidine tracts appear to have a higher repetition frequency than shorter tracts, and some may be repeated as many as 5 x 10(4) times in L-cell DNA.