The Structural and Functional Domain Organization of the Chicken Lysozyme Gene Locus

Abstract

Chromatin, the nuclear form in which eukaryotic DNA is packaged with protein, is most commonly described as a regular structure of DNA wrapped around nucleosomal histone octamers connected by histone H1—covered linker DNA regions (Richmond et al. 1983). For higher order structures this 10-nm fiber of “beads on the string chromatin”is wound into “solenoids” with six nucleosomes per turn forming a 30 nm filament (McGhee et al. 1980). In metaphase chromosomes and in parts of the interphase nucleus even higher DNA compaction must exist. Metaphase or interphase chromatin was shown to be organized in large loops at their base attached to either chromosomal protein scaffolds or nuclear matrix material, respectively (Paulson and Laemmli 1977; Vogelstein et al. 1980). How are genes organized in respect to these structures? Which chromatin conformation permits the dynamic changes that are necessary for activation and specific regulation of transcription and replication? What is the biological relevance of the loop-domain organization of chromatin? These questions must be answered if we are to understand chromatin function on the level of molecules.