My aim in writing Gene Function has been to present an up-to-date picture of the molecular biology of Escherichia coli. I have not attempted a chronological description, believing that a mechanistic account is more useful for such a highly developed field. I have divided the book into four parts. Part I is a general introduction to bacterial systems, their genetic material, structure, composition and growth. It has seemed desirable to include herein a brief preview of the remaining text, to introduce the nomenclature and to help place subsequent chapters in perspective. The expression of genetic material and its perturbation through mutation is considered in Part II. Part III discusses how the transfer of prokaryotic genetic material can be mediated by plasmids and bacteriophages. It describes the DNA transactions involved (replication, recombination and repair) and ends with a description of the genetic and biochemical techniques employed in the study of gene organisation. Finally, Part IV considers the control of expression of bacterial, plasmid and phage genes. Key reviews are listed at the end of each chapter.