The occurrence of 5-methylcytosine in DNA was first described in 1948 by Hotchkiss (see first chapter). Recognition of its possible physiologi cal role in eucaryotes was first suggested in 1964 by Srinivasan and Borek (see first chapter). Since then work in a great many laboratories has established both the ubiquity of 5-methylcytosine and the catholicity of its possible regulatory function. The explosive increase in the number of publications dealing with DNA methylation attests to its importance and makes it impossible to write a comprehensive coverage of the literature within the scope of a general review. Since the publication of the 3 most recent books dealing with the subject (DNA methylation by Razin A. , Cedar H. and Riggs A. D. , 1984 Springer Verlag; Molecular Biology of DNA methylation by Adams R. L. P. and Burdon R. H. , 1985 Springer Verlag; Nucleic Acids Methylation, UCLA Symposium suppl. 128, 1989) considerable progress both in the techniques and results has been made in the field of DNA methylation. Thus we asked several authors to write chapters dealing with aspects of DNA methyla tion in which they are experts. This book should be most useful for students, teachers as well as researchers in the field of differentiation and gene regulation. We are most grateful to all our colleagues who were willing to spend much time and effort on the publication of this book. We also want to express our gratitude to Yan Chim Jost for her help in preparing this book.

Inhalt
A chronicle of DNA methylation (19481975).- Major techniques to study DNA methylation.- Methylation of cytosine influences the DNA structure.- Methylation of DNA in prokaryotes.- Structure, function and regulation of mammalian DNA methyltransferase.- Regulation of the de novo methylation.- Effect of DNA methylation on the binding of vertebrate and plant proteins to DNA.- CpG Islands.- DNA methyltransferases and DNA site-specific endonucleases encoded by chlorella viruses.- Control of DNA methylation in fungi.- The role of DNA methylation in the regulation of plant expression.- Pattern of de novo methylation and promoter inhibition: studies on the adenovirus and the human genome.- DNA methylation and retrovirus expression.- Effect of DNA methylation on dynamic properties of the helix and nuclear protein binding in the H-ras promoter.- DNA methylation and embryogenesis.- X chromosome inactivation and DNA methylation.- DNA methylation: Its possible functional role in developmental regulation of human globin gene families.- DNA methylation, chromatin structure and the regulation of gene expression.- Steroid hormone-dependent changes in DNA methylation and its significance for the activation or silencing of specific genes.- Epigenetic inheritance based on DNA methylation.- DNA methylation and genomic imprinting in mammals.- DNA methylation and cancer.- The repair of 5-methylcytosine deamination damage.- Gene methylation patterns and expression.