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Treatment of cells with oxidative DNA damaging agents such as ionizing radiation and hydrogen peroxide produces .OH radicals which attack DNA, producing single strand breaks and double strand breaks that have a 3'-blocked terminus with a phosphoglycolate or a phosphate group attached to the 3'-terminus. While DNA strand breaks with 3'-blocked termini are the hallmark of oxidative DNA damage, the mechanisms by which such blocked 3'-termini are removed in eukaryotes remain poorly understood. The goals of this project were to identify the various genes that function in cleaning the blocked 3'-ends from DNA strand breaks generated by treatments with ionizing radiation and hydrogen peroxide, to purify the proteins encoded by these genes and to characterize their biochemical activities, and to determine the biological consequences when such damage is not repaired. Because of the high degree of conservation of DNA repair proteins between yeast and humans, and because of the ease of genetic manipulations, initial studies were to be carried out in Saccharomyces cerevisiae. The homologous genes and proteins would then be studied in humans. One aspect of our proposed research was to purify the Apn2 protein from yeast cells and to examine its AP endonuclease and 3'-phosphodiesterase activities. Apn2-like proteins have been identified in eukaryotes other than yeast, including humans, and these proteins form a distinct subfamily within the ExoIII/Ape1/Apn2 family of proteins. We purified the Apn2 protein from yeast and showed that it is a class II AP endonuclease. (Class II AP endonucleases cleave the phosphodiester backbone on the 5'-side of the AP site and produce a 3'-OH group and a 5'-baseless deoxyribose 5'-phosphate residue). Yeast Apn2 and its orthologs in higher eukaryotes differ from E. coli ExoIII and human Ape1 in possessing a C terminus that is absent from the ExoIII/Ape1 subfamily. We found that deletion of the carboxyl-terminus of yeast Apn2 protein does not affect the AP endonuclease activity of the protein, but this protein is defective in the removal of AP sites in vivo. The carboxyl-terminus may enable Apn2 to complex with other proteins, and such a multiprotein assembly may be necessary for the efficient recognition and cleavage of AP sites in vivo. We also carried out further biochemical characterization of the yeast Apn2 protein. As mentioned above, oxidative DNA damaging agents, such as hydrogen peroxide, produce DNA strand breaks which contain 3'-phosphate or 3'-phosphoglycolate termini. Such 3' termini are inhibitory to synthesis by DNA polymerases. We found that purified yeast Apn2 protein contains 3'-phosphodiesterase and 3'5' exonuclease activities, and mutation of the active site residue Glu59 to Ala in Apn2 inactivates both these activities. Consistent with these biochemical observations, our genetic studies indicate the involvement of APN2 in the repair of hydrogen peroxide induced DNA damage in a pathway alternate to APN1, and the Ala59 mutation inactivates this function of Apn2. From these results, we have concluded that the ability of Apn2 to remove 3'-end groups from DNA is paramount for the repair of strand breaks arising from the reaction of DNA with reactive oxygen species. Other studies from our laboratory indicate that the yeast APN1 and APN2 genes provide alternate pathways for the repair of abasic sites and for the repair of single strand breaks with 3'-blocked termini. The apn1 deletion apn2 deletion mutant is highly sensitive to both the alkylating agent methyl methanesulfonate and to the oxidizing agent hydrogen peroxide. While the apn1 deletion and apn2 deletion single mutants are proficient in repairing single strand breaks arising in DNA following treatment with hydrogen peroxide, the repair of abasic sites as well as of single strand DNA breaks with 3'-blocked termini is greatly reduced in the apn1 deletion.
This book is the seventh in a series of titles from the National Research Council that addresses the effects of exposure to low dose LET (Linear Energy Transfer) ionizing radiation and human health. Updating information previously presented in the 1990 publication, Health Effects of Exposure to Low Levels of Ionizing Radiation: BEIR V, this book draws upon new data in both epidemiologic and experimental research. Ionizing radiation arises from both natural and man-made sources and at very high doses can produce damaging effects in human tissue that can be evident within days after exposure. However, it is the low-dose exposures that are the focus of this book. So-called “late” effects, such as cancer, are produced many years after the initial exposure. This book is among the first of its kind to include detailed risk estimates for cancer incidence in addition to cancer mortality. BEIR VII offers a full review of the available biological, biophysical, and epidemiological literature since the last BEIR report on the subject and develops the most up-to-date and comprehensive risk estimates for cancer and other health effects from exposure to low-level ionizing radiation.
The First International Congress on DNA Damage and Repair was held in Rome, Italy, July 12-17, 1987. It was organized by the Italian Com mission for Nuclear Alternative Energy Sources. The subject of DNA damage and repair involves almost all the fields ofbidogical sciences. Some of the more prominent ones include carcino genesis, photobiology, radiation biology, aging, enzymology, genetics, and molecular biology. These individual fields have their own interna tional meetings and although the meetings often have sessions devoted to DNA repair, they do not bring together a wide diversity of international workers in the field to exchange ideas. The purpose of the Congress was to facilitate such an exchange among scientists representing many fields of endeavor and many countries. The 37 manuscripts in this volume, presented by the invited spea kers during the four and half days of the Congress, encompass the field of DNA damage and repair. They cover biological systems ranging from mo lecules to humans and deal with damages and repair after treatment of cells with various types of radiations, chemicals, and exogenous and en dogenous oxidative damages. The Congress and its Proceedings are dedicated to two international leaders in the field of DNA damage and repair, Alexander Hollaender of the United States and Adriano Buzzati Traverso of Italy. Hollaender, who died in December 1986, was one of the first investigators to recognize the damage to DNA was important in cell killing and mutagenesis. His early work indicated that cells could recover from radiation injury.
An essential resource for all scientists researching cellular responses to DNA damage. • Introduces important new material reflective of the major changes and developments that have occurred in the field over the last decade. • Discussed the field within a strong historical framework, and all aspects of biological responses to DNA damage are detailed. • Provides information on covering sources and consequences of DNA damage; correcting altered bases in DNA: DNA repair; DNA damage tolerance and mutagenesis; regulatory responses to DNA damage in eukaryotes; and disease states associated with defective biological responses to DNA damage.
This book will serve as a primer for both laboratory and field scientists who are shaping the emerging field of molecular epidemiology. Molecular epidemiology utilizes the same paradigm as traditional epidemiology but uses biological markers to identify exposure, disease or susceptibility. Schulte and Perera present the epidemiologic methods pertinent to biological markers. The book is also designed to enumerate the considerations necessary for valid field research and provide a resource on the salient and subtle features of biological indicators.
Basic Clinical Radiobiology is a concise but comprehensive textbook setting out the essentials of the science and clinical application of radiobiology for those seeking accreditation in radiation oncology, clinical radiation physics, and radiation technology. Fully revised and updated to keep abreast of current developments in radiation biology and radiation oncology, this fifth edition continues to present in an interesting way the biological basis of radiation therapy, discussing the basic principles and significant developments that underlie the latest attempts to improve the radiotherapeutic management of cancer. This new edition is highly illustrated with attractive 2-colour presentation and now includes new chapters on stem cells, tissue response and the convergence of radiotherapy, radiobiology, and physics. It will be invaluable for FRCR (clinical oncology) and equivalent candidates, SpRs (and equivalent) in radiation oncology, practicing radiation oncologists and radiotherapists, as well as radiobiologists and radiotherapy physicists.
Embracing the transformation of radiation sciences by the recent surge of developments in molecular biology, this progressive text offers an up-to-date analysis of in vitro and in vivo molecular responses in the body induced by ionizing radiation. With a unique emphasis on medical physics applications, Biomolecular Action of Ionizi
The purpose of this book is to provide an up to date review of the nature and consequences of epigenetic changes in cancer. Epigenetics literally means “above” genetics, and consists of heritable gene expression or other phenotypic states not accounted for by DNA base sequence. Epigenetic changes are now known to make a large contribution to various aspects of tumorigenesis. These changes include alterations in global and promoter specific DNA methylation, activating and repressive histone modifications, and changes in higher order chromatin structures. Each of these topics will be covered in this book.
The aim of volume 7 of Human Cell Culture is to provide clear and precise methods for growing primary cultures of adult stem cells from various human tissues and describe culture conditions in which these adult stem cells differentiate along their respective lineages. The book will be of value to biomedical scientists and of special interest to stem cell biologists and tissue engineers. Each chapter is written by experts actively involved in growing human adult stem cells.