Molecular biology. Chromatin higher order folding--wrapping up transcription.

Eukaryotic genomes are organized into condensed, heterogeneous chromatin fibers throughout much of the cell cycle. Here we describe recent studies indicating that even transcriptionally active loci may be encompassed within 80- to 100-nanometer-thick chromonema fibers. These studies suggest that chromatin higher order folding may be a key feature of eukaryotic transcriptional control. We also discuss evidence suggesting that adenosine-5'-triphosphate-dependent chromatin-remodeling enzymes and histone-modifying enzymes may regulate transcription by controlling the extent and dynamics of chromatin higher order folding.