ABSTRACT
CONTENTS 19.1 Basic Nucleosome Structure: Core Histones, Unexpected Occurrences ............................... 322
19.1.1 Histones of the Nucleosomal Core: The Conserved H4 ........................................... 322 19.1.2 Variable H3 ............................................................................................................... 323 19.1.3 Centromere H3 Histone Variant ............................................................................... 324 19.1.4 Histone H2B ............................................................................................................. 326 19.1.5 Histone H2A ............................................................................................................. 326
19.2 Linker Histone H1: A Challenging Mystery .......................................................................... 328 19.3 Transcription Factors and Chromatin Structure .................................................................... 330
19.3.1 Nitrate Assimilation Gene Cluster ........................................................................... 330 19.3.2 alc Gene Cluster ....................................................................................................... 332 19.3.3 prn Gene Cluster ................................................................................................................ 333 19.3.4 Mechanism of Chromatin Rearrangements: Toward a Genomic Approach ................ 336
19.4 Conclusion .............................................................................................................................. 337 19.5 Databases for the Aspergillus Genomes ................................................................................. 338 Acknowledgments .............................................................................................................................. 338 References .......................................................................................................................................... 338
In all eukaryotes, with the possibly lonely exception of dinofl agelates (1), nuclear DNA is compacted in a structure called chromatin. The fi rst universal level of organization is the nucleosome (see later). Other, higher levels of organization have been described. The next order of complexity is proposed to be the 30 nM chromatin fi ber. In this fi ber, six nucleosomes would be wound in a solenoidal structure, which would result in a second-level compaction. It has been proposed that the linker histone H1 is instrumental to organize the solenoidal structure. Other levels, like a series of Russian dolls, would lead to the compact structure called the chromosome. A description of different levels of organization can be found in the monographs by Wolfe (2) and Richmond and Widom (3).
