This book contains the proceedings of a conference held at the Strahlenzentrum der Justus Liebig-Univer sitat, GieSen, Germany, from October 6 to October 10, 1975. About 40 sCientists, mostly from European coun tries, came together to discuss specific aspects of modern radiation biology. The majority of the papers deal with "simple eukaryotic systems" such as yeast, algae, slime moulds etc. It was felt that these study objects offer good prospects to tackle fundamental questions. This scope, however, was never intended to be exclusive, and the reader will see from the table of contents that a variety of different systems was discussed. Therefore we thought the general title would be appropriate. The rationale that led to the planning of the symposium and the titles of the ses sions is outlined in the Introduction. We hope that this volume gathers some useful information, not only for radiation biologists, but also for colleagues en gaged either in fundamental cell research or in the application in the field of radiation therapy and pro tection. The conference would not have been possible without the generous support of the European Communities and the cosponsorship of the Deutsche Gesellschaft fUr Biophysik. If it was to a certain extent successful, then the merit goes to the very active engagement of all participants. I should like to thank my coworkers for their devoted help in the organisation, particularly Dr. Eckart Schneider, Dr. Elmar Gocke, Maria Hlawica, and Eva-Maria Peter for secretarial help.

Inhalt
On the Rationale of this Conference.- I Radiation and Metabolic Key Processes.- 1. Radiation Action on Biochemical Key Processes: An Introduction.- 2. On the Transcriptional Organization of the Ribosomal RNA Genes of Yeast.- 3. Control of DNA Polymerase Activity in Synchronized Growing Yeast after X-Irradiation.- 4. DNA-Specific Labelling by Deoxyribonucleoside 5?-Monophosphates in Saccharomyces cerevisiae.- 5. Studies on DNA Synthesis in Saccharomyces cerevisiae.- 6. Metabolism of Yeast Cells after UV- and X-Ray Irradiation.- 7. Synthesis of the Inducible Enzyme Arginase in Irradiated Yeast Cells.- 8. Synthesis of RNA after Irradiation in Resistant and Sensitive Strains of the Slime-Mould Dictyostelium discoideum.- II Repair and Recovery.- 1. Repair in Yeast.- 2. Properties and Function of Escherichia coli DNA Polymerase I.- 3. Action of Sublethal Concentrations of SO2 on Repair by Budding Yeast after Ionizing and UV Radiation.- 4. Reparable and Irreparable Damage in Yeast Cells after Low LET-Irradiation.- 5. Survival of Yeast after Heavy Ion Irradiation.- 6. Incorporation of (Methyl 3H) 5?-dTMP into DNA of Diploid Yeast Cells as Tracer of Liquid Holding Recovery after X-Ray Irradiation.- 7. Influence of Intracellular Adenosine-Triphosphate Concentration on Survival of Yeast Cells Following X-Irradiation.- 8. Split Dose Recovery and Liquid Holding Recovery in Diploid Yeast Exposed to Fractionated X-Irradiation.- 9. Repair of Damage Induced by Near Ultraviolet Light Plus Furocoumarin in Saccharomyces cerevisiae.- 10. Postreplication Repair of DNA in Mammalian Cells: A Discussion of the Mechanisms and Biological Importance.- 11. Radiation-Induced Mutagenesis and Mechanisms of Repair in the Yeast, Schizosaccharomyces pombe.- 12. Accumulation of Replicative DNAIntermediates in Response to Damage of DNA in Tetrahymena pyriformis.- 13. Recovery from Radiation Damage Mediated by Somatic Cell Hybridisation.- 14. The Effect of Liquid Holding on Survival and Mitotic Recombination of Two UV-Sensitive Saccharomyces Diploids.- 15. Over-Repair in Closterium: Increased Radio-resistance Caused by an Earlier Exposure to Radiation.- 16. L5178Y Cell Strains Cross-Sensitive to X-Rays and UV-Light: Similarities and Differences in Recovery at the Cellular Level.- 17. Detection of Hybrid DNA Formed during Mitomycin C-Induced Sister Chromatid Exchange in Chinese Hamster Cells.- 18. Dependence of Photoreactivating Enzyme -Substrate Complex Formation in Saccharomyces on Liquid Holding Treatment.- 19. Evaluation of the Action Spectrum of Yeast Photoreactivation in vivo by Means of Pulsed Dye Lasers.- III Cell Division and Progression.- 1. Effects of UV- and Ionizing Radiation on Mitosis and Enzyme Regulation in the Synchronous Nuclear Division Cycle of Physarum polycephalum.- 2. The Molecular Basis for the Control of Cell Division.- 3. Cell Division and the Effects of Cell Age upon Radiation Sensitivity in Yeast.- 4. Budding and Division Delay in Diploid Yeast after Irradiation.- 5. Synthesis of Histones in the Cell Cycle of Saccharomyces cerevisiae.- 6. Macromolecular Events Following Nutritional Shift-Up of Tetrahymena.- 7. Radiation-Induced Processes in Moss Cells: Short-Term and Long-Term Radiation Responses of Special Interest after Microbeam UV Irradiation of the Haploid Moss Cells of Funaria hygvometvica.- 8. Radiation Action on Lens Epithelial Cells.- 9. Radiation and Endocellular Control of Cell Proliferation.- Closing Lecture Modern Trends and Creeds in Radiobiology.