DNA

The objective of this study was to elucidate the
interaction of the carcinogen MNNG with nuclear DNA of Rat
Hepatoma cells. The effect of a range of MNNG concentrations
on RH cell DNA was studied by an analysis of the DNA
fragments obtained in linear alkaline sucrose gradients. A macromolecular analysis of the sedimentation profile for
0.06 mM MNNG (Experiment I), and 0.1 mM MNNG (Experiment
III), suggested that the system was paucidisperse and
contained at least three components. The major component
Max 1 has a molecular weight comparable to that known for
the mammalian replicon. Max 2 has a molecular weight
twice that of Max 1 and Max 3 has a molecular weight half
that of Max 1. The size of the replicon is comparable to
that obtained by others. Inferences were drawn regarding
the structure of chromatin and the role of the distribution
of sites hypersensitive to methylation with respect
to the oncogenes.

DNA methylation, the addition of a methyl group to the 5' position of DNA cytosines (5mC), is generally associated with transcriptional repression during early embryo formation ; however, in the adult brain, it is dynamically regulated and plays an important role in the formation and maintenance of memory. Very recently, it has been hypothesized that DNA hydroxymethylation, the addition of a hydroxyl group to methylated cytosines (5mC), serves as an intermediate in the DNA demethylation pathway. GIven its recent discovery, the role of DNA hydroxymethylation in memory has not yet been explored. In this study, we developed an immunofluorescent triple labeling protocol in order to begin examining the involvement of 5mC and 5hmC in neurons activated by consolidation of a contextual memory associated with methamphetamine in the brain's reward center, the nucleus accumbens.