Extremely underwound chromosomal DNA in nucleoids of mouse sarcoma cells

Additional DNA long-range folding is an early process during stimulation of human lymphocytes

There is disagreement about the existence of permanent single-strand breaks in the nuclear DNA of quiescent lymphocytes, possibly due to different experimental approaches. Using the nucleoid sedimentation technique, no evidence is found for spontaneous DNA single-strand breakage in unstimulated human lymphocytes and for quick break-sealing after mitogenic stimulation. An increased sedimentation rate of nucleoids, which can be monitored as soon as 3 h after stimulation, is shown to be due rather to an additional long-range folding of nuclear DNA. Such temporal folding appears to be related to RNA transcription and may interfere with detection of DNA single-strand breakage.

Age-related changes of DNA winding and repair in human peripheral lymphocytes

Superhelical density and incision capacity for UV light-induced damage have been studied in nuclear DNA of human peripheral lymphocytes as a function of donor age. With advancing age between 20 and 90 years the content of negative superhelical turns increases, whereas the ability to incise UV lesions is impaired. These data may be suggestive of an immature lymphoid cell state arising in aging.

Evidence for extensive intermolecular disulfide bonds of the proteins of non-ionic detergent high-salt-resistant skeletons of normal lymphocytes, and the altered structure in leukemia

Normal and leukemic lymphocytes were subjected to lysis with a non-ionic detergent and 2.0 M NaCl. The intact nuclear DNA and the associated molecules resulting from these lyses (the nucleoids) were then separated from DNA-dissociated molecules and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Most of the proteins undissociable by 2.0 M NaCl from normal lymphocyte nuclear DNA or from DNA-associated molecules appear to be intermolecularly S-S linked. A distinct set of these proteins was either absent or only present in greatly decreased amounts in association with the leukemic lymphocyte nuclear DNA exposed to 2.0 M NaCl. On the other hand, the opposite relationship was found for a an MW 71,000 protein with leukemic lymphocytes of every patient studied regardless of the subtype of leukemia. Conversion of normal quiescent lymphocytes to cycling cells by lectin stimulation rendered them similar to leukemic cells in some respects but not in all. Our results show an altered nuclo(cyto)skeletal structure in leukemic cells; in general the proteins involved appear to be sulfhydryl proteins whose redox states and/or DNA association properties are modified by the neoplastic transformation of lymphocytes.

Studies on DNA damage: discordant responses of rate of DNA disentanglement (viscosimetrically evaluated) and alkaline elution rate, obtained for several compounds. Possible explanations of the discrepancies

Alkaline elution is a well-known method for detecting DNA damage. Recently we have developed a viscosimetric method that is even more sensitive than alkaline elution. Here we report that the two methods, although apparently both revealing alkaline DNA fragmentation, can give dramatically different results for a significant series of compounds. We suspect that alkaline elution might reveal not only DNA fragmentation but also the extent of disentanglement of chromatin structure, whereas this DNA disentanglement rate, when evaluated viscosimetrically , is more strictly correlated with the initiation of DNA unwinding.