Carel Mulder

Tumour induction with DNA of oncogenic primate herpesviruses

THE viruses Herpesvirus saimiri and H. ateles are highly oncogenic agents of New World primates. The viruses are not pathogenic in the natural host species (squirrel and spider monkeys, respectively), but induce malignant neoplastic diseases of the lymphatic system in various other primates1,2 and in rabbits3. Marmoset monkeys (Saguinus sp.) are the most susceptible animals to tumour induction, as infection with these viruses invariably results in rapidly progressing malignant lymphoma or acute lymphocytic leukaemia within a few weeks4,5. H. saimiri and H. ateles are related viruses; they share common antigens6 and some homologous DNA sequences7. DNA from both viruses is infectious in permissive owl monkey kidney (OMK) cell cultures8. We report here that the isolated DNA from these two herpesviruses can also cause malignant tumours in animals.

Residual activity of denatured transforming DNA of Haemophilus influenzae: A naturally occurring cross-linked DNA☆

Abstract The residual activity of denatured transforming DNA of Haemophilus influenzae is accounted for by the presence of cross-linked molecules in all DNA preparations, whereas single-stranded DNA has no detectible transforming activity. The specific transforming activity of the cross-linked molecules is at least 90% that of native DNA. This conclusion is reached from the observation that the residual activity sediments 1.3 to 1.4 times faster than the bulk of the denatured DNA through an alkaline sucrose gradient, almost identical to the rate of an artificially cross-linked DNA. Similarly, the residual activity is eluted from a Sepharose column 1.5 times faster than the bulk of the denatured DNA and almost identical to the elution pattern of added native DNA of the same homogeneous size. Moreover, the buoyant density in CsCl of the molecules carrying the residual activity was found to be close to that of native DNA and considerably lighter than that of denatured DNA; with denatured biological hybrid ( 15 N 2 H 14 N 1 H ) DNA, this fraction was found only at a buoyant density slightly heavier than native hybrid DNA; no activity was found near the densities of native or denatured heavy DNA or native light DNA. The intrinsic residual activity is equal for all melting conditions tried and for nine different markers studied. It was found to be 11.5% for a DNA preparation with an average molecular weight of 30 × 106 daltons, and it is linearly related to the molecular weight of the DNA. Therefore, it is estimated that about three cross-links are present per bacterial genome if they pre-exist in vivo.

Relative locations of rearrangements in the DNA of defective simian virus 40 (SV40).

Abstract Electron microscopic examination of linear heteroduplex molecules was used to investigate the position of deletions and substitutions in SV40 DNA. Two plaque-purified samples of SV40 were serially passaged three times at high input multiplicities and compared to a sample serially passaged at low multiplicity. Viral DNA was extracted, and closed circular molecules were cleaved with the RI restriction endo-nuclease. Heteroduplex molecules were formed by denaturation and renaturation in formamide, and each sample scored for rearrangements. The first high multiplicity virus stock had a 100-fold lower specific infectivity than the comparable low multiplicity stock; 8% of the DNA molecules in this sample were resistant to cleavage by RI restriction endonuclease. An additional 6% of its DNA molecules contained sequence substitutions, deletions, or insertions. These rearrangements seemed to be located throughout the genome. Six percent of the DNA molecules from the second high multiplicity virus stock were resistant to cleavage by the RI enzyme and an additional 25% of the molecules carried rearrangements. Two principal classes of molecules with rearrangements were observed in this sample, the major being a simple substitution originating at 0.26 fractional length unit from the RI site and replacing a segment of about 1.4 × 105 with one of 0.87 × 106 daltons. A second rearrangement was found in which the substitution of a sequence of 0.14 × 106 daltons for one of 1.5 × 106 occurred at a position 0.27 fractional length from the RI site. These molecules contained in addition an insertion of 1.05 × 106 daltons at a distance of 0.05 fractional length from the end of the substitution.