Distribution of DNA damage in chromatin and its relation to repair in human cells treated with 7-bromomethylbenz(a) anthracene

Abstract

We have examined the relationship between the distribution of DNA damage and repair in chromatin from confluent human fibroblasts treated with the carcinogen 7-bromomethylbenz (a) anthracene. Analysis of staphylococcal nuclease (SN)4 digestion kinetics and gel electrophoresis revealed that more total damage occurs in nucleosome core DNA (approximately 80-85% of chromatin DNA) than in SN sensitive DNA (APPROXIMATELY15-20%). Furthermore, over a 24 hr period, damage is removed at about the same rate from these two regions. In contrast, virtually all of the nucleotides incorporated during repair synthesis are initially SN sensitive even when measured at 12 hr after damage. With time many repair-incorporated nucleotides become SN resistant and coelectrophorese with nucleosome core DNA. To explain these data we propose a model whereby excision repair occurs in both linker and core DNA; however, in core DNA the repair process induces conformational changes resulting in temporarily increased SN sensitivity; subsequently, rearrangement occurs and results in the re-establishment of native or near-native nucleosome conformation and SN resistance.

Formation and Repair of Psoralen-DNA Adducts and Pyrimidine Dimers in Human DNA and Chromatin

“…4). Bromomethylbenz(a)anthracene, in contrast, forms more adducts in core DNA than in linker DNA (40). These results contrast with those previously observed with UV light, in which pyrimidine dimers were found randomly in different nucleosomal regions (34).…”

“…This randomization did not appear to be caused by any of the major metabolic processes associated with DNA (e.g., replication, repair, transcription, protein synthesis). The excision of pyrimidine dimers similarly occurs at the same rate from different regions of chromatin (34), as does excision of 7-bromomethylbenz(a)anthracene adducts (40). 5).…”

Chemical carcinogens: a review of the science and its associated principles. U.S. Interagency Staff Group on Carcinogens

“…Therefore, in the near term, it is expected that integrated exposure assessments (utilizing monitoring data, results from physical and chemical models, and considerations of all routes of exposure through all media) will be conducted on a case-by-case basis (see pp. [248][249][250][251].…”

“…A preliminary assessment using available crude data can often shed light on the upper or lower bounds of potential risks (see pp. [248][249][250][251].…”

“…Principle 23. An exposure assessment should describe the strengths, limitations and uncertainties of the available data and models and should indicate the assumptions made to derive the exposure estimates (see pp. [251][252].…”