Bacterial Chromatin

Abstract

this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission from the Publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work.Cover illustration: H-NS-DNA complex visualized using scanning force microscopy (Courtesy of R.T. Dame)Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com) v PrefaceThe birth and the development of molecular biology and, subsequently, of genetic engineering and biotechnology cannot be separated from the advancements in our knowledge of the genetics, biochemistry and physiology of bacteria and bacteriophages. Also most of the tools employed nowadays by biotechnologists are of bacterial (or bacteriophage) origin and the playground for most of the DNA manipulations still remains within bacteria. The relative simplicity of the bacterial cell, the short generation times, the well defined and inexpensive culturing conditions which characterize bacteria and the auto-catalytic process whereby a wealth of in-depth information has been accumulated throughout the years have significantly contributed to generate a large number of knowledge-based, reliable and exploitable biological systems.The subtle relationships between phages and their hosts have produced a large amount of information and allowed the identification and characterization of a number of components which play essential roles in fundamental biological processes such as DNA duplication, recombination, transcription and translation. For instance, to remain within the topic of this book, two important players in the organization of the nucleoid, FIS and IHF, have been discovered in this way. Indeed, it is difficult to find a single fundamental biological process whose structural and functional aspects are better known than in bacteria.However, a notable exception is represented by the physical and functional organization of the bacterial genome. Although some bacteria contain more than one chromosome and some chromosomes are known to be linear, the majority of bacterial cells contain a single circular chromosome. The chromosome of Escherichia coli consists of about 4.6 million bp corresponding to a fully extended circumference of about 1.6 mm and rapidly growing bacteria may contain up to almost four genomic equivalents. Thus, the need for compaction of this genetic material to fit within an approximately 500-fold smaller volume is obvious; likewise, also clear is the need for a dynamic "chromatin" structure capable of undergoing rapidly all kinds of vital transactions to respond promptly to different types of environmental cues, changes and stresses with focused and/or global reprogramming of gene expression. All this happens within one or a few ill-defined structures called "nucleoids" where the cellular DNA is localized.The ...